Just another update in case anyone stumbles upon this. I got 7 cards working finally. I found my Win10 install was in legacy mode, not UEFI.

I ended up making a UEFI Win10 USB install drive. Reset the bios. I set the internal gfx to be primary, as once I installed one or more cards I was getting a triple beep. Got it all installed (and fought my way through all the win10 setup again, (updates, start menu not working, etc.).

So I have 7 AMD cards working on this motherboard with Win10 UEFI install (1709). It's running well and stable. So all in all, once I figured out what I was doing, it is a good value board.