I have dual R9 390 cards driving 3x Asus MG279Q displays on Windows 10 64-bit running Crimson 184.108.40.206. The Skylake-based CPU's iGPU is driving two other monitors as well. I have attempted the following steps multiple times, always with the same result:
Although I see 2 of the 3 MG279Q monitors show the Windows boot logo they go blank in Windows. At this point the system would be unusable except for my Intel-connected monitors. Although Device Manager reports 2x 390s in the system the Radeon utility won't run. Windows reports only the two Intel connected monitors as well. Going back to step #1 and repeating the cycle results in the same outcome.