I have set wit dual RX 570 with ubuntu 16.04 installed. If I detach any of the graphic cards everything is running fine. But if both of them are attached black screen appears just after selecting OS. I have 17.40 AMD drivers version. Interesting fact is that I'm not able to install Ubuntu with both cards attached either. Depending on version I receive kernel panic or never ending fast scrolling console output. Windows installer starts properly in this set. I can install unreleased version of drivers if it is necessary (I'm able to rebuild OS config in 40 minutes so I can risk).