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AHCI is supported out of the box on Windows Vista and later, Linux-based operating systems (since version 2.6.19 of the kernel)
Windows XP and older do not provide AHCI support out of the box.But if you check out the relevant topics,you will see that it's not an issue.
Your chipset supports ide technically,but as it seems Asus has decided to opt it out.Just Raid and Achi options are available (manual)
Adding and/or changing bios modules/options may not give you what you are looking for
PRIME X370-PRO

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you should update your bios then edit your bios settings then,could be the better path here
MMTool Aptio 5.02.0024 Mod
microcode,modules etc
AMIBCP 5.02.0031
edit settings

Hex Editor (online)
MCExtractor for microcodes.see cpuids,platform numbers and check if they are up to date
How to manually extract/replace/insert BIOS modules
How to flash a modded AMI UEFI BIOS

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a modded version of the previous MMTool v5. does not trigger my antivirus.false positive anyway

So, it's not about the setting being hidden in the bios and just requiring an edit to show, or to force enable it through the AMIBCP tool, I'd need to insert a module in to my bios (in this case, update my storage controller) for it to work, as the code for it to work may not be there and not just deactivated?

Am I understanding you correctly?

thats the case,adding ahci/ide or finding if its locked away is not that easy as you can see from the tool.and even if you do find and succeed,it still may not work

but you are welcome to try,use AMIBCP 5.02.0031 and see if it is locked if you can find it,fix it.

since you are going to flash it (given that you have succeeded) use MMTool Aptio 5.02.0024 Mod as well and update microdoces,modules etc.

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@Mikedebian

You risk bricking your system if you mess up a BIOS mod.

I would suggest a JMicron PCIE card

https://www.ebay.com/itm/PCI-E-PCI-Expre...ZgAAOSwhcJWNqgZ

with IDE BIOS mod (comes configured in RAID by default)

https://onedrive.live.com/?id=4F7BE65BF6...F7BE65BF6B6294F

and the firmware update utility -
https://archive.org/details/ftp-driver.jmicron.com.tw

not necessarily.changing a setting or replacing a module should not brick it,and most of the time it is reversible.risky? yes though
windows may not boot from pci card,and that's also possibility.depends on board.again generally speaking
windows will boot into ide without a hitch
booting from ide to ahci is the tricky one

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