I have 2 R9 390's in my pc. but crossfire works on like 1/100 games.
more I have :
ASrock Combo-G h110m
1000watt Corsair psu
well and 2 sapphire nitro R9 390's
Not all games support Crossfire, and that board's PCIe x16 physical slots run at x16 and x4, which doesn't really work, since the 390 uses PCIe for Crossfire instead of an external bridge.
but it actually works in some games like GTA 5, Rocket League, Tomb Raider etc. but (mostly uPlay games) it doesn't work.
Retrieving data ...