I have 6 rx 470s on risers running on a z170a motherboard. The issue I'm having is if I use one video card, everything runs nicely. 4 or more it gets crazy, in the sense that I have the following problem. The computer boots but everything is pitch black on the desktop like in the photo:
http://i.imgur.com/taSyK47.jpg

If I go into the bios and turn off Above 4G Decoding then the computer will boot fine and show all cards with exclamation marks, turn it back on and i'm back to sq one. I have tried setting the PCIe to gen 1 and gen 2, I've updated the bios, I'm not sure what else to do. If you have any suggestions, please offer them, thanks.