Disabled 1 or 2 peripherals in the BIOS. Not much available. And no change. Still only 4 GPUs. According to GPU-Z. And the device manager has one Unknown Device.

Forum thread has people saying Windows 7 can do 5 GPU or more.

https://bitcointalk.org/index.php?topic=103244.20
https://bitcointalk.org/index.php?topic=188334.0

Sure ain't working for me though. Might depend on the AMD driver version?

Found this. May try w8. That might give me 5. Or even 6 with additional tweak.

https://bitcointalk.org/index.php?topic=215987.0