I’d just play the chosen audio to the one soundbar and simply ‘group’ it with your other soundbars, using the Sonos App, to play to all.

 Do you know if each soundbar works as the main one? I need to work in 3 different rooms whit the same spatial effects.

No you’d just get stereo output for the TV audio to the grouped rooms.

You would need to ‘extract’ the audio output and split it over a cable-link to get surround audio… something like a 3-way optical splitter/extractor will give you 5.1 surround sound audio.  

OP needs to clarify whether the source is TV, streaming audio from a atmos source, or something else.  If you’re talking about streaming atmos music from Amazon Music for example, then you can simply group the audio.

If your talking about TV audio, I would assume that the 3 separate rooms also have a TV?  In that case, I would have all 3 TV use the same source via an HDMI splitter, than each TV can send audio to the soundbar it’s connected to.  I wouldn’t use Sonos grouping feature at all for that scenario.

Actually I may have to stand corrected here - I’ve just grouped two Sonos Arc’s and a Beam (gen2) here and played the Movie ‘6 Underground’ from Netflix and my "now playing" screen shows this…

So you may need to just double check this with Sonos Staff - but looks like it’s working here for surround sound from both TV and Music audio sources.

I should add that I only had the movie displayed on the one TV screen in the primary room - ‘Kitchen’ (obviously) that was using a Beam (gen2) attached to the TV - the two Sonos Arc’s in Living Room & Dining Room were outputting to each Soundbar, Surrounds & their Subs.

So I’ve learned something there - every day is still a school day.

Actually I may have to stand corrected here - I’ve just grouped two Sonos Arc’s and a Beam (gen2) here and played the Movie ‘6 Underground’ from Netflix and my "now playing" screen shows this…

So you may need to just double check this with Sonos Staff - but looks like it’s working here for surround sound from both TV and Music audio sources.

Surely that TV audio badge only relates to the Audio In for the soundbar, not the grouped soundbars.

If you play a Dolby Atmos TV source and group a non-Atmos room, the TV Now Playing screen will still show Dolby Atmos badge.

The post filter on this community is now a joke.

Edit: my earlier post has gone to a mod for approval

Yes of course, I’m sure you’re correct @Mr. T as the main HT room is still outputting TV Surround sound in this situation. Admittedly though I was initially surprised by what I was seeing and hearing with TV audio across the group - hence my suggestion to run this past the Sonos Staff.

I was taken back by the fact that I did have sound outputting from the rear surrounds and Sub in the two Arc rooms. I was expecting to hear nothing from those surrounds.

So ‘Yes’, it’s clear now that the ‘grouped’ TV audio is stereo to the two Arc rooms and they’re playing as grouped (music) audio - I do have the surrounds set to ‘Full’ audio for music output and that’s what was confusing me initially.

If I play Atmos music audio from Amazon to the group I see Atmos Audio badge too and if I group-in a Beam Gen1 (a fourth soundbar) the badge switches to ‘Ultra HD’ - not that it adds anything here.

So just for your benefit @FILIBAO - when the three (compatible) soundbars are grouped, any Atmos music audio (from Amazon music for example) via the Sonos App, will output in Atmos format to all the ‘grouped’ soundbars - if you were to then group-in a non-Atmos speaker, the audio on all players falls back to stereo.

TV surround sound audio/video will play on the primary soundbar only and display on its connected TV screen - the two other grouped soundbars play in stereo only. There’s a slight delay to the grouped rooms between 75ms and 2s - depending on settings set in the Sonos App - the stereo audio can be set to ‘Full’ output to play on both the ‘grouped’ Soundbars and their Surrounds/Subs.

I hope that assists.

To achieve 5.1 surround sound audio output to all - you would need to look at a wired option using an audio extractor/splitter - the easiest option is a 3-way optical splitter…but note this is just a solution for ‘audio’ output/input only. 

Thank you.

each room has a synchronised projector, so i need a e-arc connection in each room? 

If the Projectors do ‘sync’ in some way themselves, then isn’t it perhaps easier to just cable a Sonos soundbar to each one and have them play the TV A/V source in sync? The current soundbars support an HDMI ARC/eARC or an Optical connection (with an adapter) - the latter does not provide TV Atmos output, but all support compressed 5.1 Dolby, DTS surround sound  - Note that HDMI eARC is needed for uncompressed TV surround audio: Dolby TrueHD, or Multichannel PCM.