I must agree too Z170 chipset is having problem with 3+ cards on most boards, its prolly bios related, but who ever is doing testing first disable all non needed IO and internal devices as:
- sound
- ports
- any add in hw as firewire, wifi, etc
- set PCI-e to x1 mode if possible
And only then test it, also better use win10 because it should handle 8 GPU with no moded drivers
Ill give it a try, however i just cannot wrap my head around the fact that the z170 chipset has more pciE lanes compared to the h80 or h97, in every single connectivity feature the z170 is superior to the h97, and somehow the former performs much worse than the later.
I guess that it is a hardware issue, but mostly a uefi issue, so maybe a custom rom or manufaturer update will solve this, however i wasnt able to fin any information of anyone trying to develop a custom rom for that purpose. And the bios updates do nothing regarding the 6 gpu compatibility issue.