I'm guessing you mean trademark, not copyright -- copyright does not make sense in the context used -- but I'm not sure why you think it would be trademark infringement.

My guess is they are referring to the similarity between the name Sonos and SonoBus.

Absolutely. Almost certainly problematic as one of Sonus’ leading value props is exactly this function - audio sync across their ecosystem.

if they want to keep it, they should come up with a viable long term business model, because obsoleting hardware isn't it. otherwise their threat hopefully will vaporize eventually, along with their non-ip stranglehold.

perhaps they meant something like “hmm, couldnt streaming copyrighted music using this app constitute a violation of rightsholders' intellectual property?”, which, on the one hand: haha; on the other hand: lmao

I was about to write a comment about how I'm not supporting a company that ruined by Google Home speaker group functionality so yeah I think Sonos would have a pretty good trademark infringement case here.