They are both connected to the video card. If I were starting over, retracing my steps, I would say 1. Disable secure boot for initial install 2. Install updated AMD drivers. When computer reboots... 3. Enter bios and re-enable secure boot. 4. Let computer complete windows startup. Of course, I took the long long way to do this so I'm not absolutely sure it would work. This seems to be the path though. The enabling of the on board video adapter was just a diagnostic step so I could see what was going on. 
I got a Yeston RX 550-4G D5 LP graphics card. When I install there is no output to my monitors. The HD light flashes and from the sounds it is booting normally. From what I can tell the PS is sufficient for this card. I can't tell from the spec sheet or user's manual if there is a compatibility issue. Any help/advice appreciated.
XPS 8700, Yeston RX 550 4G D5 LP, no display