@Lost_N_BIOS: The System did and does pass POST. And it also boots up with install media and did also support two windows install runs.
So I did not think that the Bios could be related to any of the encountered problems first.

@Fernando:
1. Not at that time. I was led to this thread by @Lost_N_BIOS.
Installing the INF-inst-utility is what I had been doing after new windows installs since my P4 or Core2-Systems (so for about 15 years or so, I've been doing this on windows installs).

2. The above mentioned is part of the explanation for this point also.
On previous win-versions and hardwares, the chipset components often weren't installed/listed properly in the device mangager, lots of them with exclamation marks as unknown (pci-)components.
So it has become a routine to check wether the chipset components are "installed" seemingly correctly or not.
Plus, in this particular case, I felt encouraged through post #23 also, so, even after reading your start post there, I later decided to give it another try to install it anyway.

3. I did install it because I had thougt that I could implement a native Intel AHCI Driver file this way, since the controller is part of the chipset.
After finished initial Win10 install, I looked in the Device Manager Tab and noticed that the chipset components had already been identified and listed, so I did not need to install anything for those.
But instead of the "Intel X79/C600 Sata AHCI Controller", there was merely a Microsoft-branded "Standard AHCI Controller" installed/listed in the Controllers section.
I had expected that if I chose to add an inf-package that was not needed, the system would discard or omit it anyway and at solely install the "correct" AHCI controller drivers.
I was not sure if the intel RST packages were explicitly for raid use or for usual single-volume AHCI also, so I tried out the chipset-packages first.

4. I did install it by using setup.exes if the packages came with one. I also used the method of pointing to the .inf files manually later.

5. Why "Several Versions": I used the latest (2013, for Win7 and 8.1) packages provided by Asus, then I tried to DL a package from intel, and finally I tried a package found in this forum.
I did that because trying to install the diverse sata driver packages provided by asus or intel (RST) did refuse to install ("wrong platform") or Win10 stated that there was a "better driver already installed".

And I used the manual method you described also.
Since the system has not started up for several days now and I had tried to install drivers for the further not recognized onboard components afterwards; plus I had to fix my attention on another operation on my main system in the mean time, so I do not recall anymore if the Intel AHCI driver had been accepted or not.

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At this point, I am not even sure why the system won't start up at all.
I had encountered a not identical, but, looking back on it, similar appearing problem when I had installed win10 on that system the first time.
Installation was successful, but after some boot-ups (with me trying to install the ahci drivers) the win 10 system wouldn't start up and shortly after that the Bios began to warn me about a SMART fail of the system drive that was in use; I had thought that the failing of the first win 10 system was do to harddisk failiure.
But if I look at it now I begin to question wether it could be some sort of hardware issue.
The board and installed memory had been in use for 11 months only and had then been stored away until I had began to build up a system a month ago. So I did not expect that any damage could have occured on board and dimms in the mean time.

@Fernando:
It may be a problem with the onboard marvell sata controller.

I have tried several win10 setups in the mean time and I created a recovery point right after first boot-up and basic settings.
I let the chipset inf files untouched, as win10 seems to install own ones after some time.
I included the intel rst driver found in this forum during the win10 setup procedure, which speeded up the setup time dramatically.

The only item which remains with an exclamation mark in device manager is the marvel 9128 sata controller.
First it is listed as unknown sata controller, later as standard sata ahci controller. But alway with warning, that the device cannot be started.
This does not change if I deactivate the marvell oprom in bios setup at all.
If I replace the driver with one mvs91xx.inf, the device name changes to "Marvell 91xx SATA 6G Controller" and seems to be ok.
But from this point the option fields in the controllers device manager tab to update the driver files or to remove the device are greyed out an inctive.
If I try to start the "scan for new hardware" funtion, the system keeps on scanning to infinity. The next boot-up ends in the hang that I experienced earlier.

In the end, anything that I try that is related to the oboard marvell controller results in the system hang I described earlier.
It is of no matter which mvs91xx.inf file I use (win 7/8.1 from asus webpage; or the ones provided in this forum), it triggers this system hang which I can only fix by reverting to that recovery point.

As for now, the only option seems to be that I simply don't use the marvell controller, whis is not that much of a problem.
But I can't remove the driver or device permanently, since it keeps on coming back even if I deactivate it in bios.
This could trigger further problems, if future windows updates would try to update that driver also, I suspect.

What I still don't understand is why it makes the system hang so badly, that it cannot repair the error by itself.

@Fernando:
I have no devices connected to that controller.

This topic developed somehow while the thread progressed.
First it was about that I wanted to provide @Lost_N_BIOS with a bios region dump from the X79-WS Board.

I wanted to test any bios mod on that board first before I use them on my current system (X79E-WS Board).
-> But I had to get a system running on that board. To use the Intel ME Engine for the Bios Region Dump.
-->I decided to install win10, so I could try this out too, before replacing the OS for my current system.
--->And then, while installing ME and vendor driver files on win10, the problems with the system hang began.
---->Until yesterday, when I could locate the marvell controller or the respective driver(s) as source of the problem.

And the qustion how to fix this problems developed as a side effect*shrug*

@Fernando:
I had "let it flow" because I did not expect the problem to grow so big and time-consuming and because I found the provided information useful to get this win10 system running.

I am still interested in
a) make the amsedia/iocrest nvme controller working on my systems (this was the initial problem and relates to nvme booting).
b) explore the possibilities of adding bitfurcation funtions to my X79/C600 systems, as @Lost_N_BIOS and I were talking about.

So of course, it is not my decision to make, but you could crop the thread so that strictly the nvme-bitufurcation-biosmod related content remains.
The cropped parts could be edited/transitioned into something else - I don't know, maybe there is still some information contained in it that some-one else coud find useful in the future?

@Lost_N_BIOS - I will try out your modeded capsules on my P9X79E-WS board and will report on the results.
Well, if the machine should boot up after the procedure. If not, a response could take a few days.

I used this method to get bifurcation functional on P9X79, however I havent been able to enable the bios menu.

@Fernando - I'm not a fan of split topics "just because" during progression of the discussion all for the same user/board covers multiple topics, so I'll leave that to you, since we all probably have differing opinions on stuff like this.
To me, this leads to broken discussions for no reason, and may confuse future readers following along.

I always use chipset.exe -overall too, on all clean installs, it's a thing since forever

@paranoid_android - you and Fernando's discussion has lost me what's going on now, so not sure where you are or what's going on anymore?
I'm still ready to build both BIOS for you, but unsure what's going on, this has taken forever so I can't even remember if I've already done the mods or not, but do remember I was waiting on dumps form you for both systems for some reason, instead of sending you stock mod BIOS.
Now, I think maybe we don't need dumps, since we'll use USB Flashback instead of FPT.

@JackSted - I just saw your thread too. this can all be done via other easier BIOS modifications, but your end result may be similar/same. Once we get to that here I'll be sure to tag you again so you can see final outcome BIOS and maybe test it if you want.

@Lost_N_BIOS Id love to help test the end result for the bios however I have neither P9X79E-WS or P9X79-WS im on a P9X79 so unless its no extra work to add that model to the assemly line I can't help test.
However im eager to learn easier methods to replicate my result.

Less work more better :D

@Fernando, it's not about difficult to do in my eyes, only about splitting up the flow of thoughts, I rarely see that as ideal to do, unless people start talking about a party in town or something totally unrelated to computer stuff already being discussed. To me, this is all related, so I would have never considered splitting anything up.
Same applies to title in my mind, all still remains the same, and we will continue towards that goal quickly now I hope, and with success eventually of course I don't see the title misleading at all, still going 100% in that direction except a short side-track we've all taken part in this past few posts.
Cutting up threads all the time breaks peoples flow of thoughts/effort progress, and then topics loose their overall knowledge for others later in the future. If anything was split off, that would be an added thread in the forum for no reason, and no one would ever post in it again or read it etc.
But, those are only my opinion on all this, I'm sure everyone has varied opinions on how things should be done

@JackSted sorry, I missed your board variant. Yes, once we do it all I'd be happy to show you what to change where, or port over a mod for your model as well.

@paranoid_android - did you test via USB Flashback the BIOS in post #26 yet, if yes and both worked, which method do you prefer then I will do for both boards

@Lost_N_BIOS: You're absolutely right, it took forever ;)
I have revieved two cap files from you for the P9X79E-WS Board.
You did add Nvme Boot and Bifurcation.
One version contains both system agent sections, one conatins just the previously hidden one.

I will try out the one with both system agent sections first via Bios flashback.

If all works, I would want to get the other board's bios (P9X79-WS) modded also.
I had sent you a bios region dump of that board.
Then, as troubles with the latter board and win10 setup began, I sent you my own nvme-modded 4901 Bios as cap file to inspect.

What I would request is that you could apply your bitfurcation mods to this bios also? Somewhere at that point we lost track.

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Plus, I have a Z9PE-D8 WS here, a board with at least two completely independent and unswitched x16-Slots.
That would just per perfect for housing one or even two fully loaded Asus Hyper M.2 Cards.
I am not planning on using 8 NVme SSDs at his point, but the option of disabling some or even the most of the onboard sata controllers is very tempting.
With this Z9 Board it might be more difficult to implement mods, as it is a server/workstation board for Xeon E5?