Sorry for the late response ... moved on to issues with AMD cards :-)
Here is my reply from another post. Let me know if you need further details:
Try this ... it worked for me to get all 6 cards working:
Reset the BIOS by removing the battery
Update the BIOS if you have not already (you can do this before or after the resetting)
Boot the os with 0 GPUs connected and change your BIOS settings to mining mode and use the onboard VGA (IGFX)
1 by 1 install the GPUs rebooting in between ... not sure this is necessary, but it worked for me
THis worked for me in SMOS (or linux), so I hope it works for you as well. Basically what was happening is that there was a collision at the kernel level with this mobo trying to output video from card 1 and the IGFX because you may have booted the machine with a GPU installed int he 16x card slot. At least that's what the system messages in the LInux OS told me.
Good luck mining ... especially after the ETH difficulty increase :-(