That's right but in my defence that's really a 3.1 system as you have lf, rf and center in a single speaker. It's also worth to note that lf, rf and center speakers are the most demanding/used channels so IMHO the problems were avoided not fixed. Putting all your channels into a single speaker is not really what I thought when I heard of wireless multi-channel audio.
I also don't know what resolution they use because it's not mentioned in their specs but something tells me it's not 24 bit at least not for the separate speakers.
I've tried multichannel wifi audio but it just doesn't work either due the buffering or the sync issues. I ended up with some proprietary technology with multiple antennas based on the 5GHz band but you need clear line of sight and that's not always convenient. Anything obstructing the line of sight may make your speaker fail to play.
To sum it up: it's true that sonos has a 5.1 system but that's really a half backed solution. It's actually a 3.1 configuration. This may work for some people just like bluetooth speakers work for so many. Can they play in a real/native 5.1 configuration(6 separate speakers)? that's hard to say. What about real 7.1 or the latest configurations such Atmos/DTS:X ( 5.1.4 or 7.1.4)? That's impossible without hardware changes.
Some would say that even standard ethernet is not good enough for multi channel audio(thus avb[0] or [1]powerlink) so I can't really see how standard wifi could work.
[0] https://en.wikipedia.org/wiki/Audio_Video_Bridging
[1] https://en.wikipedia.org/wiki/Ethernet_Powerlink