I think, problem is in your adapter.Use HQ adapter (active adapter is preferable) or appropriate HQ HDMI - Displayport cable (as short as possible)
Awesome, bought 2 hdmi x displayport cable and I still can't get to 2560 x 1080.
One of the monitors allow me to go 3840 x 2160 while the other won't let me past 1920 x 1080.
And great news: I can't connect my 4th monitor at all - it only allows to have 3 active monitors.
Really, what am I doing wrong? I have 1 hdmi x hdmi cable and 3 f*cking displayport x hdmi cables and only ONE monitor is working fine, what the hell AMD? Plug'n'play not a thing anymore?
I am afraid to answer you but i have read some info and it looks like, that for your configuration you need active DP to HDMI adapter.
I am not 100% sure and please don't buy anything until you will be sure, that it will work.i don't want to be responsible for your next loss of cash
Maybe someone else here will confirm this info...