I don't have that specific motherboard; but I have other z97 mobos with similar 6 GPU difficulties. I will get one out and see if I can find the problem tonight.
To help me find the problem:
press f12 to open the guake terminal
If cpuminer-opt is running rightclick over the guake terminal and select new tab or press ctrl + c to stop it.
then enter:
lspci | grep VGA
please tell me what this outputs
00:02.0 VGA compatible controller: Intel Corporation Xeon E3-1200 v3/4th Gen Core Processor Integrated Graphics Controller (rev 06)
01:00.0 VGA compatible controller: NVIDIA Corporation Device 1c02 (rev a1)
03:00.0 VGA compatible controller: NVIDIA Corporation Device 1c02 (rev a1)
06:00.0 VGA compatible controller: NVIDIA Corporation Device 1c02 (rev a1)
07:00.0 VGA compatible controller: NVIDIA Corporation Device 1c02 (rev a1)
09:00.0 VGA compatible controller: NVIDIA Corporation Device 1c02 (rev a1)
lspci doesn't see the GPU because the riser wasn't plugged in on boot. If it was plugged on power up and boot, would get error 55 and the system wouldn't even boot neither would get any video or interaction, hard reset is the only option there. The problem is not in the riser or GPU or slot because this is happening on all 5 rigs (z97x and 1060), replacing risers, GPU or power cables doesn't help.
I'll try now to leave it past the bios and then plug in the sixth riser on GRUB choose.