I've heard some chatter about some "low end" motherboards being designed to only support two graphics cards. The LSI manual says this, "Note: Some PCI-E slots support PCI-E graphics cards only; if a RAID controller is installed on those PCI-E slots, it will not function." My motherboard manual says, "This motherboard has two PCI Express 2.0 x16 slots that support PCI Express x16 2.0 graphics cards complying with the PCI Express specifications."
So far LSI support as just said, "The motherboard listed is a gaming motherboard designed for multi-gpu usage. These slots are most commonly dedicated for video and would be the source of the problem. I would recommend attempting to use the controller in a server class system to correct the issue."
How do I sort out if my P7P55D PCIe slots are "graphics only" or "real" slots?