I'm using the same USB image I used originally, but it's not "modified". I've been reading about using rufus to create an EFI image, but I'm struggling to re-find that info. I'm not confident it will make a difference, as the USB stick worked the first time through. Maybe I'll try the DVD ROM drive - I was trying to limit my SATA devices. Would this be worth trying?

I do have BIOS CSM set to enabled, Boot Device control to "UEFI and Legacy OPROM", Network Device to "Ignore", Storage Devices to "UEFI driver first" and PCIe Expansion Devices to "UEFI driver first", as outlined in post #124.

I can ask on the NVMe thread - my concern is that I expect I'll get suggestions that are not possible with the P9X79 motherboard (with it's board-specific settings), but it's worth trying, I guess.

It should work then, was trying to think of things that could be causing issue. On SATA, yes, if you mean hard drives, there should be none attached other than your NVME. I know how you had those settings set that I quoted, since I quoted your comment, I asked if those are in-line with what the guide says to set for each

That thread, is specifically made for your situation, same method covers all/any board this modification is done to, nothing there is board specific.
[Guide] How to get full NVMe support for all Systems with an AMI UEFI BIOS

Finally, the magic happened!
I formatted the USB stick as GPT and recreated the install media from the original installation DVD (both with Rufus) and booted off it. The USB stick shows up in boot options as a UEFI drive.

The first install screen (32bit vs 64bit install) shows up as a small window on the monitor - a noticeable difference from booting before, but once the graphical installer is running it goes full screen.
I definitely had to let the installer create the partition(s) and not diskpart, but that was easily figured out when it stopped complaining that the NVMe drive wasn't a bootable drive.
I have no idea why it had to be a GPT USB stick the second time, but that was the deciding change. Win10 is now happily booting on my NMVe drive.

Many thanks to Fernando and LOST_N_BIOS! Your help was much appreciated!

@xmetalloid - finally, you got it!

Correct - I now have an entry named "Windows Boot Manager", but that wasn't until I managed to get the Windows installer to recognize the drive as a bootable device and install onto it - I wasn't getting that far originally. The reason I put the device named "PATA SS:" as the first device is because this appeared to be the hardware device I wanted to install onto - I thought it would cause the BIOS to recognize it as a boot device. I wasn't wrong, but it didn't help.

The key to success was using a GPT formatted USB memory stick. For some reason, the installer needs to be on this, in order to get the installer program to recognize the NVMe drive. Bizarre, but at least it works now. I have no idea why I didn't need to do this before (I didn't even realize you could format a 16GB USB key as GPT). Even the original DVD install disk wouldn't work.

In case anyone else has hit a wall, they might want to try this before giving up. The mention of formatting a USB stick as GPT was buried in pages of discussion about the history of AHCI and NVMe. It is NOT contained on the many brief instructions on how to install Windows 10 on an NVMe drive or how to modify an unsupported BIOS. It didn't seem to be an issue for anyone else getting the error message I was getting. I suspect others may have experienced the same thing, but gave up already and are only using the NVMe drive for storage.

Hello. I'm new here and i have a problem with Marvell esata controller. In windows 7 and 8.1 works perfectly fine the eject but not on windows 10 even with the latest drivers. I don't care about Nvme and ME. Should it be safe to update with this modded bios?

Heya, I know this is fairly old, but any chance you could whip this up for the 'P9X79'? There are tonnes of deluxes and pros but nothing for the basic iteration of the board.

@sese - PX79 and PX79 LE use exact same BIOS, I compared in hex byte-for-byte same, and exact same recovery/flashback name due to same BIOS. I believe I've NVME Modified both and uploaded here, but since so many mentions of other similar models I cannot locate either due to limited search
But as mentioned above, it's easy! If you can't get it, let me know I will redo for you and post here for the next guy looking too.

@Fernando all I have to say is WOW. That tool is very straightforward and worked perfectly. Generated the latest and greatest with everything I wanted. I also appreciate that the OP of such a beauty tool was the first reply to my first post on the forums :) As the IT dude for many years I know this place well but only ever really HnR'd. Will stick around going forward :)

@Lost_N_BIOS Appreciate the info! I plan to dog food this myself before sharing, but it really does seem straightforward, and safe with USB flashback :P

@sese glad you were able to do it yourself and found it so easy! Now, once you've tested your mod BIOS, if you want you can upload and post here to share with the next one looking that maybe doesn't think it's so easy to mod themselves

I await his post with his comments. In my participation on this thread, I found most of the work to get a modified bios pretty complicated and tedious. Were it not for the clear and direct guidance offered by Lost-in-Bios and Fernando, and complex tasks Lost-in-Bios did for me; I would not have been able to get my P9X79 Pro to use the Pcie M.2 SSD.