Try those settings:
1) Make sure you're running the latest BIOS!
2) Enable 4G
3) Set PCIe support to "Auto" - DO NOT MANUALLY SET TO GEN1. THIS CAUSES MAJOR ISSUES
4) Enable onboard graphics startup as first! I believe this is changing "PEG" to "IGD" or something in the Advanced BIOS
5) Plug your monitor into the ONBOARD graphics
I should have mentioned this, but I did set them all up like this. I also have had 7 cards mining on one board, although only for a few minutes before I restarted the rig to continue troubleshooting.