When I add my ceiling speakers, I have Netflix Atmos support on my Apple TV 4K, but I use my Sony 4K player for discs. I wish my Firestick 4K had support as that is my favorite streamer and remote.
In order to get Dolby Atmos from Netflix and Amazon, I have to use HDMI ARC and stream to the TV. I do not get Atmos from my 4K HTPC. The HTPC will stream a 4K picture though. Interestingly the ChromeCast Ultra from an Apple iPhone will stream Atmos. I have not tried either of my 4K disc players, a Panasonic and a Sony.
The good news is that the HDMI audio return on 4K devices works perfectly, much to my surprise, and is very easy to use. I just press the Netflix or Amazon buttons on the TV remote and select TV audio on the pre/pro remote and it works.
Amazon has never worked well for me as far as audio is concerned until this new 4K system with audio return and now it is very good.
Actually this ARC system on 4K systems has probably been the greatest benefit. I find the increase in PQ detectable but marginal. The increased SQ from Netflix and Amazon has been dramatic. I think there is a deliberate downgrade, especially from Amazon when not using an App.
By the way talking of PQ and audio quality, the Detroit Symphony Orchestra moved up to 4K via Facebook Live last year. They have simplified their mic arrangement and now just use three spaced omni mics and NO spots, not even for soloists. The sound and picture is absolutely superb. I steam that via my 4K HTPC.
I have always favored simple mic techniques over complex ones. That is what I always did for my broadcasts. Far better results are obtained compared to a forest of microphones. Although the latter can help poorer systems, and the former really allow good ones to shine.
These DSO streams from 2019 and 2020 until Covid 19 shut everything down are just staggeringly good, especially with the new Dolby upmixer. You absolutely feel you are there.