Gigabyte X58A UD3R not working with AMD RX cardsa

[Willemcross]

Hello guys, I was wondering if somebody could help me here.

I have a Gigabyte X58A-UD3R motherboard (rev 2.0). This board on the current bios is the FH released in 2012/01/06. On this BIOS both RX 480's that I have (Sapphire Nitro RX 480 4GB & ASUS DUAL OC RX 480 4GB) do not give display outputs. In my main build with a MSI Z97M motherboard the cards function correctly. With a GTX 1060 my X58A posts just fine, no problems whatsoever.

I was wondering if there is a way to mod the bios so that RX 480's give display output. It apparantly is possible to get a RX 480/580/5700(XT) working on this board, if I look up test results on userbenchmark.com. 

I couldn't find a specific bios-mod-request section for GPU-related things so I'd rather ask it here.

I'm unfortunately not experienced with updating the bios and all the things about bios modding, so any help with that would be apreciated.