They can’t be added to the same Sonos ‘room’ that has your surround system is in, but physically, you can put them anywhere. When you ‘group’ the rooms, any other room will be at least 75ms behind your PLAYBAR’s room, but only when playing the TV input. They’ll be in sync when streaming music.

I suspect your speakers are being impacted by wifi interference , causing interruption in their connection to your router. 

Beyond the suggestions in the linked FAQ, I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

I have already contacted Sonos ! They told me it is not possible to ad speakers without interference to my setup because of software limitations, Sonos says this is normal because this is an older system ( ? ) . That’s why I am reaching out.

Temporary software or WiFi problems aside, you should be able to group another speaker with a surround room, even if the heart of such a room is an older soundbar. I’m surprised the Sonos employee told you this would not be possible.

It looks like there’s been a S2 software problem with the Playbar for a couple months: 

Your problems looks different because it only happens when grouping, though. Maybe call Sonos again?

Still … I asked twice and both times Sonos told me I could ad the speakers but interference will be normal ??? 

Everything used to work just fine, maybe it’s a problem with S2 … thinking of downgrading to S1 … would this be a good plan ? I have a set up with older hardware so it should work fine !?