Greetings,
This is possible on Intel based boards, I have never done so on a AMD chipset. I found posts on AMD's forums from a large number of users that state it isn't possible. I do not know if this is true. I also have not found any documentation on the registry entries which dictate the driver the OS will use for RAID with an AMD based board. Intel yes, AMD no.
Appreciate it if you would try and post your results. I'd start with a full disk image back up. This way you can experiment without data loss.
I know you said you have 2 disks connected and configured in BIOS for RAID in the RAIDExpert Utility, that's fine.
Try this:
Download the pre-install driver:
https://download.gigabyte.com/FileList/Driver/mb_driver_579_x64_9.3.0.221.zipYou'll need to run the .exe and save to a directory or USB stick
Now open MSCONFIG, select the Boot tab and enable the SAFE boot check box, apply and close. Don't restart here.
Now use the start menu to restart the system. Enter BIOS, Change the controller operate mode to RAID. F10 to save and allow the restart. Windows should boot. If it does, try updating the storage controller driver to RAID.
Now restart again and verify the RAID driver is loaded. If satisfied, disable SAFE Boot in MSCONFIG and restart normally.
At this point, I would install the RAID Expert2 Utility which will give you enhanced support, management and array recovery options. It should pick up your existing array assuming your have it enabled in BIOS, have marked the member disks, set the RAID level and created the array properly.
Troubleshooting:
Things that might go wrong. After enabling RAID, the BIOS may set the boot order incorrectly. Ensure your m.2 drive remains first.
Installing the RAIDExpert2 Utility prior to upgrading and changing the controller's operate mode may be wise.
Final thoughts:
This might not work. I have never tested it. Will be interested in hearing your results. Worst case, you'll have a back up to revert to should things not turn out well.