Ok, so I have a R9 Fury X and three LG Ultrawide monitors (21:9).
One of the monitors is connected through a HDMI - Displayport cable (the Insignia one that comes with the graphic card) and it works fine.
The second one is connected HDMI - HDMI and it works fine as well.
The problem happens when I try to use my HDMI - HDMI cable using a HDMI -> Displayport adapter. It won't let me set the monitor at any 21:9 resolution - it actually recommends 16:9 as its native resolution.
Things I've tried and didn't work: many different HDMI cables; swapping which monitor is using the HDMI port (which means both monitors are working fine).
What I think the problem is from what I read about: either I'm unlucky and all my cables are HDMI 1.4 (and seems like only HDMI 2.0 supports 16:9) or the adapter is messing it up (not as a malfunction, as I have 2 adapters).
What I was planning to do: buy a HDMI - Displayport cable that runs up to 10.8 Gbps bandwidth and seems to support up to 2560 x 1600 (16:10). It makes sense to me that this same cable would support 16:9 but I can't confirm this information anywhere.
Can someone help me out, please? I don't wanna buy 2 cables only to find out they don't work