Hi...
You can either have either of the connection side by side covering half screen each or one covering the whole middle.
In latter case if your single signal is not wide enough to cover the whole screen you will have black bars on either side.
I have basically the same question as N0ddie but I'd just like to check if you do the same thing with a PC inputting at QHD? If I have a game my GFX card cant run at the full superwide (a GFX upgrade + G9 is crazy money) DQHD, is it possible to just drop it down to QHD and play the game in the middle of the screen as though its a 27"? Everything ive seen about this just references consoles so I wanted to double check.