Not on windows 11 so can’t check exactly but on windows 10 you just right click on the speaker icon in the tray then click I think sound properties or device properties. Something like that, there are only a couple of menus for the audio. In the main menu where you select the device underneath you should see a drop down menu, it will likely say stereo and when you expand it there will typically be stereo, 5.1 and 7.1. Select 7.1 and your audio issue should be solved.
As for the colours, I have no idea about SLI 3090, have actually never heard of anyone running them let alone so niche as the 8K X. Is it possible in software to just use a single 3090? I could imagine that would be causing major issues, also afaik the audio also goes through the DP now using nvidia DP audio or something so that could possibly be causing audio issues if changing the channel to 7.1 doesn’t solve it.
The colours not adjusting and being reddish/brown is a first, I’ve helped quite a few with issues but never heard of that one before so my immediate instinct is that SLI is causing it but honestly just a guess.