Hello Phnx,
I was actually getting the same issue in my struggle to setup a RAID 5 as well.
I *think* I resolved it by replacing the power supply with a intel 4xxx series compatible power supply. If the issue creeps back in this is something you might consider.
thinking about it a little ( since its been a few weeks since I had the issue ) , I think I experienced it when I installed Windows using the "F6" option drivers. That isn't required since Windows has drivers for the chip-set built in since Windows 7.