Just to add , I have the Asus A8N-SLI , It only has 4 SATAs. I was also stuck with I think is the same type of problem. It appears that the BIOS can only see 6 drives at a time, On the 7th drive the BIOS just hangs. I have tried many different combination of PCI cards and PCIe cards and with IDE hooked up or not. I always get the same conclusion that only 6 drives will boot up.I did a BIOS update and that didn't matter. I even pulled all the cards, hooked up 4 IDE and 4 SATA and still hung until I pulled out any 2 drive and then it worked.
I gave up on this board and bought a P5B-VM DO and it works great.
-Schmall