That’s an interesting question. I suspect we won’t know until until the release of S2, which should be soon. However, the previous streaming to a Sonos device has never included an option for Dolby Digital except through  the digital line in...so I have my doubts. I hope to be pleasantly surprised.  

Can you post a link to this article you are referring to? I’d love to read more about how they’re compressing that into a music stream. 

I haven't read the full article so I'm not sure how deep they get into the spcifics.

I first saw the article at  

The Verge and again at Forbes

Worth reading the Reddit linked article in that Verge piece;

https://www.reddit.com/r/Android/comments/84y5md/psa_about_atmos_for_mobile_devices/

The Verge article suggests:

You’ll also need a streaming device that both supports Atmos sound and has Tidal. Devices that meet those metrics include the Apple TV 4K, Fire TV Stick 4K, Fire TV Cube, Fire TV Stick (second-gen), Fire TV (third-gen), or the 2019 models of the Nvidia Shield TV or Shield TV Pro. Sony and Philips smart TVs that support Atmos and run Android TV will also work without the need for a set-top box.

which suggests it will be going through the TV connection anyway, which would allow the Arc to use the ARC or eARC connection, and nit be streamed directly to the Sonos system. 

The article then goes on to suggest that: 

Assuming you’ve got all that set up, Tidal will automatically stream the Atmos version of a song or album, assuming there’s one available. Tidal also will label available songs with a “Available in Dolby Atmos” tag, and users can search the phrase “Dolby Atmos” to specifically find compatible tracks. Additionally, Tidal is also curating dedicated “At Home” playlists featuring Atmos tracks.  

Which suggests to me that there are extraordinarily few of these Atmos music tracks available. 

This seems like a marketing ploy by Tidal to me. 

sigh.. you probably right. 
Fortunately I have no plans to keep Tidal, figured I try them out since I have a 2 month free trial.

Nothing wrong with a free trial. But I’d be interested if you’d report how many albums are available in an Atmos mix. 

Duh!

Why haven't I don't that already.

I counted 35 playlist and posted the screen shots. Seems to be a nice collection of different genres.

There is a few more playlist but you get the point.

Now mileage per playlist varies.

The. First playlist creatively titles "Dolby Atmos" has 16 tracks.

 The Pop play list has a whopping 57 tracks!

I spotted a couple playlist such as 3 Doors Down that only had well 3 tracks.

I'll play with it when I get ARC which I finally pre-ordered by the way but I waited to long. Anticipated ship date is the 19th vs the 10th.

Atmos music doesn’t make a ton of sense to me, for a couple reasons.  The first being that 99% of the time, the artist or original producer didn’t create and record the music with Atmos in mind.  It wasn’t even created in sound surrround, but in stereo.  So someone else has decided how to modify the audio so that certain sounds come from the ceiling or from the rear, but it’s not what was originally intended.

The second reason is that no one every experiences live music in Atmos sound.  Musicians are on a stage in front of you, not strategically placed all around you.  In this way, our brains sort of expect to hear music from the front only.  I think that’s different when it comes to audio accompany video because it’s not just music, but everyday noises as well.  It makes sense to hear a plane flying overhead, etc.  It even makes sense to hear music coming from different directions as it’s meant to be background and not the focus of your attention.  Or to provide a more immersive effect.

That said, I can see some tracks, something like like Bohemian Rhapsody perhaps, being great with Atmos, since it has so many different parts, changes in tone, etc, which would perhaps makes some sense to come from different directions.  As well, in order for new tracks to be specifically developed for Atmos, there has to be an initial baseline.

The documentation for SMAPI makes no mention of adding Atmos support, but it could be a “secret” S2-only addition. Without SMAPI support no music service can stream it to Sonos devices.

https://developer.sonos.com/build/content-service-add-features/supported-audio-formats/

To me, music in Atmos is a lot like music in quadrophonic. Interesting, but not sustainable as a listening staple. Even 5.1 music, while it’s out there on DVDs and some TV channels, hasn’t been pervasive enough to change everything. YMMV. 

The implication in the articles that were linked above is that the input would be coming in to the Sonos Arc via the ARC or eARC connection, so not ‘native’ to the Sonos app. 

I don’t think it makes a lot of sense to support Atmos music ‘native’ at this point, since only Sonos rooms with Arc would be able to play the content in something other than stereo.  The advantage would be that you could theoretically play music in several rooms, stereo or atmos where appropriate, in perfect sync (no TV audio delay for grouped rooms).  That would  be a plus, but seems like a lot of effort for a feature that isn’t going to be highly desired right now.