I and many others would just like uncompressed Dolby Atmos passthrough.
That is not possible on anything other than a BluRay disc where the audio is embedded into the record.
However compressed passthrough of lossless Atmos files would be viable with MAT 2.0/2.1 if you're into ripping BRs & using your own Plex media server. Compressed passthrough is virtually lossless, but not inherently so in its origin; slight, but important distinction.
Why 100% uncompressed is not possible is because most streaming platforms (ATV+, D+, Netflix, HBO Max) use Dolby Digital+, or the eAC3 codec to stream their Dolby 5.1 & Dolby Atmos files. There is a way to bypass this (a la the Dolby Access app on Xbox Series X allowing for Upmixed audio--permanent MAT container across the UX), but this would require Dolby certification of Apple's SoC.
We know Apple's secure & private practices regarding their tech; closed, end to end. I don't see Apple sending off an ATV device off to Dolby engineers to have a look inside the SoC. That would open up the possibility for reverse engineering.
To make that work would require a hefty amount of corporate cross-talk between Apple & Dolby. No doubt an expensive ordeal to arrive at an agreement, with NDAs to boot.
I want it as much as the next ATV user, but I'm not sure if Apple would spend the money on this specific "problem," for which in their mind already have it covered in the form of connecting the ATV directly to your soundbar / AVR--as another user here mentioned.
There is an exception, or caveat--ALAC--but I'm not sure how viable the codec would be for streaming in tandem with video. In theory, ALAC--currently used for Apple Music--could work since it can transport spatial audio metadata, and supports 16-bit/44.1 kHz through
24-bit/192 kHz. Bear in mind, this codec is used in individual files that carry audio only no longer than a few minutes [songs].
Changing the container for which Dolby 5.1 & Atmos files are carried would be different when taking into account the considerably larger file sizes due to them also being comprised of video. ~20, ~30, ~50 minute files for episodic media, and 90+ minutes for films.
To execute this would require a ton of backend work from not only Apple engineers, but also every single streaming platform (Netflix, D+, HBO Max, etc) to achieve compatibility, which once again poses one large problem: money.
It
can be done, and there are multiple solutions, but any which one would require significant resources.
The best we could hope for is bitstream passthrough, which would put an end to audio delays & lip-sync / audio latency issues. This would be the simplest & cheapest, and would also allow for lossless passthrough of audio data within BR rips via PLEX, but not through the mainstream streaming platforms.
For those who choose to connect the ATV directly to their tv would require a tv with HDMI 2.1 & eARC with features such as Bitstream Passthrough on the tv itself for this to work properly. It would
also require a soundbar or AVR with HDMI 2.1 & eARC as well. There are plenty of soundbars on the market with eARC, but the pool of products is significantly smaller with
AVRs. <-- Link to a Yamaha RX-V6A AVR.
