What Apple TV generations support airplay and surround sound through airplay?

Hi, thanks for this answer.

I was aiming at the exact same setup as OP: an Apple TV 4k plugged to a projector, streaming (hopefully surround) sound to Sonos (Beam Gen 2 soundbar and speakers) via Airplay 2.

It is disappointing if audio streaming from Apple TV only allows stereo then... Where can we read about this? I can't find any information about the supported audio formats of Apple TV 4k and Airplay 2 anywhere...

Is there any way you would suggest for achieving a similar result: wireless surround sound (to Sonos or others) from a source like the Apple TV 4k?

Does that mean Generations 3 and earlier support airplay 1 or original only?

Yes. The 2nd and 3rd generation model support original AirPlay 1 (not numbered back then).

AirPlay system requirements - Apple Support

An older version of this document was more detailed on differences between original AirPlay vs. AirPlay 2.

I am wanting to connect my Sonos surround sound system via airplay through the Apple TV.

That won’t work. See below.

I know Airplay 2 supports surround sound

It’s a bit more intricate than that. Users can AirPlay-stream video with surround sound to Apple TV, but streaming audio from Apple TV to AirPlay speakers will be in stereo.

For surround sound, you will want a wired connection. Depending on your setup, you may need an audio extractor adapter.

The only exception is the large HomePod speakers, which can virtualize surround sound (still two speaker units after all).