Of cource i use the latest bios, because without it you can run only 4 gpus. I made a lot of different tests yesterday and now i can say - only 6 gpus can run on msi z170a m5. I also have two z170 gamimg pro carbon, may be it can runs 7 gpu, but i dont beleave it )
hi free riser card / gpu
http://gpufarm.xyz/product/z-pci-e-1x-to-16x-powered-usb-3-0-extender-riser-adapter-card/