Yeah, Sonos is very much the Apple of this space. A solid, user-friendly implementation of several pre-existing concepts into a cohesive product - no small task. I don't think the technologically important parts of this are patentable though, there's both prior art and the obviousness standard to worry about. But very much like Apple's 'rounded corners' case, they've gone after (IMO) obvious UI functionality for such a system to extract money from their competitors.

If you are just interested in the synchronized Audio-over-Ethernet part, AES67 is the industry standard, and a pretty complete open-source implementation can be found at https://github.com/bondagit/aes67-linux-daemon , though AES67 is itself a composition of existing standards, fundamentally it is mostly composed of SDP for sessions description, RTP for media, and PTP for clock sync, so you can build that out of a variety of implementations too.

For room correction you can look at https://drc-fir.sourceforge.net/ to generate FIR filter coefficients, then you can apply it in realtime with https://github.com/wwmm/easyeffects or https://github.com/HEnquist/camilladsp .

Of course some people just want it to work, then you can shell out for Sonos :p.