Am I doing something wrong? I see many people here running 6 X RX480 on the BTC PRO MB and Win7 and Win10, I have the same setup using powered risers and with 6 cards can't even get to post. Most I got working is 4 cards. I have the MB running 295 X2 GPU, 3 of them for a total of 6 GPU's fine, but no dice with the 480's. Am I missing something?
Are you using powered risers? They are needed if running more than 2... maybe 3 cards. The MB can only supply ~150W to PCIe slots. Cards can draw up to 75W from the slot (though 66W or less is more recommended...). It would be an issue, especially if using 6 pin rather than 8 pin PCIe power connector 480s.