I was hoping you will get in touch on this issue The good news is that 1st problem is now resolved. You've got me thinking once the provided test file didn't produce expected results. To clarify, for the best 4K HDR picture quality I'm using MPC-BE and MadVR combo. I was convinced that my audio setting are taken care off to handle Dolby Atmos - apparently that wasn't the case. I have played test file with PotPlayer which immediately showed Dolby Atmos on LED. So I headed back to MPC-BE and updated not only MadVR audio filter settings to output all Dolby and DTS format but player itself had to be also updated - basically same setting in 2 places and voila Dolby Atmos from MPC-BE. Checked with test file and some movies (oh boy, Baby Driver first scene is just perfect for such test). Audio experience changed dramatically with the correct DA being played.The LED screen will only scroll Dolby Atmos once, when you start playing Atmos content. Try downloading https://download.dolby.com/us/en/test-tones/dolby-test-tones_9_1_6.mp4 and playing it from your PC and from USB on your TV, and see if you get the screen to show Atmos with that.
Anyway I hope that someone will find this useful. Now I need to solve issue 2. As described only eARC showing on display but not Dolby Atmos. I suspect that HDMI cable is to blame. Honestly I don't remember now but I think the only 2.1 certified cable seats between PC and Q950A.