I have had similar problems with getting a gigabyte board to run in AHCI mode. It is the GA-MA 780G board, which is fairly well documented on the net. It does exactly as you suggested and the only way it will work is if I switch in bios to IDE mode.
I understand that there is a workaround once you boot into windows, but I don't recall the details. Like I said it should be pretty easy to find in any search engine.