I have found it! It WAS a setting in BIOS.
If anyone else is having trouble finding it, it was...
Main -> IDE Configuration
with the following settings...
Onboard IDE Controller [Enabled]
OnChip S-ATA Controller [Enabled]
SATA Mode Select [SATA Mode]
also, nVidia RAID function [Disabled] -- but I suspect that can be enabled without conflict
Hope that helps someone, sooo glad I finally found it.