Do yourself a favour and configure it on a linux machine.

Use kernel parameters to disable ACPI and self-assign IRQ's to each GPU (ACPI can stuffup horribly for some reason with so many GPU's)

Ive had 8 GPU setup like this temporarily but it really puts alot of strain on the board and I could literally feel the slots heatup with all 8 running thus I dont really support this for a stable longterm setup.