I went through the same mission with that motherboard. After weeks of hairpulling I came across the solution. You need to do this to the two slots marked PCIEX8.
https://bitcointalk.org/index.php?topic=102547.0
Hope I was able to help
https://bitcointalk.org/index.php?topic=102547.0
Hope I was able to help
I haven't had any problems with my GPUs being detected. They're always there in the device manager. I think this solution is for when a MoBo isn't seeing a GPU at all, isn't it?