With the S2 app, Sonos currently supports 24-bit/48 kHz audio from Qobuz, so I would imagine the Port would eventually be able to support Apple Lossless at 24-bit/48 kHz too. But Apple Hi-Res Lossless goes all the way up to 24-bit at 192kHz which I doubt Sonos products can support.

The only Sonos product that currently supports Spatial Audio/Dolby Atmos is the Sonos Arc. And this is only supported through an HDMI eARC connection.

Do you mean there would be a need for update, or will work just right now? Also, do you mean I should use S2 app to stream in order to get lossless, or I can play directly from Apple Music?

Apple Music Lossless is not currently supported by Sonos, but hopefully it will be supported in the near future. Read more here:

With Qobuz, you can currently stream 24-bit/48 kHz audio from the Sonos app. Hopefully this will be possible with Apple Lossless too.
https://support.sonos.com/s/article/1782?language=en_US

Apple Music Spatial Audio/Dolby Atmos is currently supported by the Sonos Arc through the Apple Music app on an Apple TV 4K and an eARC connection or HDFury Arcana.

I got a Port (through rca) to Marantz and BW 606. I played Apple Music on Sonos app, will be lossy again and then I played same track from music app on the iPhone via Airplay. With Airplay there isn’t full hires, but a lossless limited to Cd quality, for me? Airplay with lossless sound better, detailed and more spacious than aac via Sonos app.

I clearly hear the difference between Dolby Atmos and regular lossless streaming through Sonos Port directly from Apple Music. Which quality is better, is debatable but what I can say Dolby sounds less harsh, less distorted to my ear. There is a playlist on Apple Music for Dolby version of songs: https://music.apple.com/ca/playlist/jazz-in-spatial-audio/pl.efbd24628ff04ff3b5e416a6e237d753
 

In order to test, I turn on/off Dolby from Setting → Music 

I agree, I definitely hear a significant difference turning it on/off AND IT WILL STAY ON FOR ME!

We have to wait lossless on Sonos app now AirPlay is good

I’m mistakenly marked this as an answer 

What would be the advantage of Sonos app over local Apple Music player? Why even use Sonos App and ad d an extra step?

Sonos Port has got own Dac 24/48, right for hires music. The advantage of Sonos app the streaming comes from Apple Music server, to Sonos Device it sound like Spotify connect or chromecast. With Airplay the transmission pass through iPhone to Sonos Port and it is limited to 16/44. With Sonos app you can turn off your phone, with Airplay both devices has to be linked. I hope to explain, sorr for my nglish I reply from Italy

For me the only benefit of using the Sonos app besides managing system settings is choice of multiple music sources/playlist libraries in a single search, but not all will give lossless or Dolby Atmos playback! As much as I am enjoying the difference of Apple Lossless/Dolby Atmos I am mostly just using Airplay from the Apple Music app. That’s just me. I am sure others may have a different desire and different reasoning. 

Good point. Thanks.

I thought AirPlay 2 is capable of delivering 24/48, unless Sonos Port doesn’t receive it at its end?

I appreciate the response by srefanomas as it taught me some valuable and useful technical stuff. I may now lean more towards using the Sonos app first. (Although searching won’t show the lossless/Dolby Atmos tag that shows in the Apple app.)

What I know that Qobuz stream on Port hires 24/48, on native Sonos S2 app and I hope in the future Apple Music do the same. I’ve already sent a request to Apple Music support. Sonos is the only one that has got Apple service in own app and introduce the lossless must be the next step. Thank for your reply