16:3 Aspect

Ok so ... lets clarify:
a) you are preparing a composition of 16x3 aspect ratio (3x4K horizontal) with 11520x2160resolution - ist that correct?
b) you have issue with setting up a composition like that or you did set that composition like that, made all animations and after rendering it compresses everything to 16x9 aspect ratio?
c) if technical setum let you use only 2K resolution as a maximum why not to try to 2048x384 - the maximum horizontal resolution that you can output on hardware that you have. That way your render will be much faster and also outputing hardware will apreciate not resizing of huge 3x4K video file to 1x2K

Ok, the (kind of) solution was really easy.

I made a composition 4k output and just resized all the content in there, it seemed a bit deformed but at the displays they where just right with the right margins. The videowall splitter has an output of 2k regaddles of the video so it doesn't matter if the final project didn't have the 4k res at the end (after the deforming PAR). I know its not the best outcome but it solves a momentary problem.

How do you even intent to playback such a huge file? It might help to actually read up on the capabilities and limitations of specific video formats. Of course nothing stops you from customizing your settings, but then attempting to play back a possibly uncompressed file won't do you any good, either. It really comes down to you having to educate yourself.

Mylenium