Have been reading back in the threads a few weeks but haven't found anything that I haven't already tried or specifically related to my mb and gpus.

Asus Prime Z270-A
GeForce GTX 1070 Windforce OC 8G x6

Updated BIOS on the MB
Disabled Sound
Power ON after power loss selected
On board graphics - Enabled selected IGFX
All PCI speed to Gen 2
Above 4G Enabled
ASPM is Disabled
Plugged into the onboard graphics via the HDMI port

SMos boots from my 128G USB2 pen drive with the NV version but see's only 2 of the 6 GPU's.  I've unplugged all but three for now.  If I can get 3 going I'll move on to 4 and so on.

I've checked all my risers and cards and they all work in Windows 10 but also not at the same time.  Just fyi I also had an MSI Z170A SLI Plus and sent it back thinking it was a mobo issue.

Has anyone had any success with this board and gpu combo yet?  If so what am I missing or not setting correctly in the BIOS?  On the PCI speed I've tried all settings... Auto, Gen1, Gen2 and Gen 3.  The setting listed above are what I have set currently.

Thanks in advance for any and all help.