How can I get 2560X1080 resolution on my LG 29UM58 monitor, connected to a Mac Mini? I just bought the LG 29UM58 21:9. My computer is a Mac Mini late 2012 (i7 model) running OS X 10.11

The display preferences just shows 1920x1080 16:9 than then is stretched out to 2560x1080 21:9. 

SwitchResX software doesn't work? (Crashes? Runs but doesn't offer other resolution choices?)

I use a Thunderbolt to HDMI adapter. 

How can I configure better resolution choices (ideally 2560 X 1080) for my setup?
You'll need a 1080 capable adapter or better. See this thread for some options. 


How can a Mac mini drive 3440 pixels wide display instead of 1920?


I'd get the cable matters 4K adapter over the 1080p one if you can afford the extra $4 cost. 

Keep in mind HDMI spec as well for limits on resolution: Can a MacBook Air support 2560x1600 output via HDMI using a Mini DisplayPort/Thunderbolt to HMDI adaptor?