So I can't get both AHCI AND RAID ?!
I dont think so. Unless you have TWO SATA controllers in your mobo.
How about this...
Set AHCI on. Once in Windows
Go to Disk Manager
Change the both of 1TB hdd disk type to Dynamic
Create a Mirror volume out of these TWO drive.
This is pretty much the same thing that you're trying todo
software raid mirror, instead use intel raid drivers now you use OS raid