Okay so I can almost 100% promise you that you're limited to 2ch because of CRU. (It sounds like you're literally walking in my footsteps from ~1 yr ago).
When I was trying to do what you're doing with CRU, for whatever reason, that would mess with the audio drivers and would limit output to 2 ch. someone with more background on driver software would need to explain why that is, but it would work every time I reinstalled drivers after messing around with CRU so I believe that's what causes it.
There are a couple work arounds... The most straightforward is to actually get a DisplayPort to HDMI adapter and use the DisplayPort output for audio and the hdmi you're using now for video. That will enable you to do more than 2ch while using CRU (at least this is the solution I read and saw confirmation that it works. I honestly got as far as buying the adapter and realized the marginal benefit moving from 1440p to 1620 or 1800 wasn't worth all the dicking around, so I never actually hooked it up, but it should work).
Lastly, DD/DTS isn't really a thing in PC games. Generally everything is multichannel PCM, which is good, because it's uncompressed (versus DD and DTS, which are heavily compressed). I think there might be one or two games that are starting to natively support Atmos, but everything else is MultiCh PCM. Once you get the audio issues sorted per above, that's what you should see popping up on your AVR.