You may want to continue using the SATA controller in RAID mode, AHCI will do no good.
If Windows* does not see the data, it is possible you will get better results when booting into a Linux* Live-CD so you can attempt to save the files into a different drive. You can try this option first as it is probably the safest.
You may also get into the RAID Option ROM by pressing Ctrl+I and reset the disks to non-RAID. Theoretically, this will not destroy the data in a RAID 1 array but will remove the RAID structure just in case it became corrupted. However, this will probably not help if the issue is with the GPT.