Taichi x399 cannot install windows in RAID mode

I'm chiming in after another weekend of troubleshooting. I'm afraid I don't have anything great to report, but some validation that could still be of help.

I had no problems with ghost arrays in UEFI, creating and deleting arrays was pretty reliable, as long as I saved and rebooted to UEFI after each such operation. I still could NOT for the life of me push the windows installation to go through on a target drive, a single drive configured as a "Volume". This is the configuration that is expected to be set when you want to create a JBOD array. Perhaps that is the caveat, this array only has one drive, and thus might not be "Enabled". IF that is the case, there is no obvious way whatsoever to leave a single volume outside of a RAID array, while in RAID mode.   

It didn't work either when I tried installing windows on this drive with no arrays created yet. 

Looking at the RAID config table in the docs (the one you posted here), I also did not like the known issues listed. Given the trouble I had with RAID, what others reported, and the reliability issues listed, I decided it would be wise to give up and not trust my data to be safe on this garbage implementation.

I switched back to SATA and windows is running smoothly. I'll think of another way to secure my data from drive failure, like investing in a small NAS. If I had worked for the time I took troubleshooting this, I would have earned that NAS already.  As for i/o performance, I'll have to do without it, or buy a RAID card later.

 One thing I did notice when I installed my system in SATA mode is that the one HDD that was part of an array was being read by Windows as a partitioned disk, and nothing I did would restore it to a single drive. none of the windows utilities could do anything about that. I ended up installing Minitool partition Wizard and was able to convert my drive back to a GPT volume, enabling all 8 TB as a single drive. I think the array creation process might leave behind some metadata on the drives that cause windows' disk management tool to report undesired drive profiles. Is that fixed with the RAID drivers installed? I don't know, food for thought. I suspect the weirdness you are seeing in Windows has to do with bad drivers/UEFI RAID software, rather than a hardware issue on your motherboard. But why not RMA it if you still can...

Good luck guys!