I'm currently trying to get up to 8 GPUs to work with the Asus Z9PE-D8 WS motherboard but have come across a blocking problem. It boots fine with 6 GPUs composed of three AMD Radeon HD 7990s (each consisting of two AMD Radeon HD 7970s) taking up PCI-E slots 1, 3 and 5. However when I occupy slot 7 with either a single GPU 7970 (giving a total GPU count of 7) or a dual GPU 7990 (giving a total GPU count of 8) the motherboard fails to boot.
With 7 it gives qcode 5A which means 'Internal CPU error' and then cycles through qcodes 5A - 32 - 4F - 63 - 70 - 79 - 94 - 95 - 19 - 5A a few times in a loop until it gives up and shows the following message on screen.
With 8 it fails to boot giving qcode 94 which means 'PCI Bus Enumeration' and then does nothing.
Clearly it's run out PCI resources. But can anyone shed light on what the intended behaviour and use of this motherboard is in terms of number of GPUs supported as well as ways to overcome this problem? I tried to get in touch with Asus via the web but their support website (vip.asus.com) was done and upon calling them I was told by a recorded message that for component support I would have to contact them online. Dead end. Has anyone else got experience with this motherboard and have you had better luck with >6 GPUs? Thanks.