After waiting for the announcement for Echo integration with Sonos for what seems like an eternity (I was really looking forward to it), I have to say I am somewhat underwhelmed by the current offering. For what it's worth, here's my feedback: -
A glorified Bluetooth speaker - is what it feels like. I could have done most of what I'm currently getting by putting a cable from my Echo Dot to my Sonos Connect Amp's line in. In fact I tried that some time ago but quickly disconnected it as the streaming TuneIn Radio via the Echo cuts out a lot more than the TuneIn Radio via Sonos, and I listen to radio probably 90% of the time.
Everything is through the Echo - as above, it seems you're not controlling Sonos through Alexa at all, you're simply outputting Alexa audio through Sonos. When that's TuneIn Radio, it cuts out just as bad as when using just the Echo. If I could hard-wire my Echo I would, but it's WiFi only, and it's 4 feet from a Google Wifi hard-wired WiFi point, so the network connection to it can't really be improved upon. My (hard-wired) Sonos very rarely drops out, but when I say "Alexa, Play BBC Radio One in the Kitchen" it starts, but drops out a lot. Which makes me think it's the Alexa source, not Sonos's own, that it's playing. This is (to me, at least) confirmed by the fact that you can't access local libraries, Spotify or Deezer. It's crippled by only being able to access (surprise, surprise) Amazon Music streaming service.
So...all it's really good for at the moment (IMHO) is start / stop, as long as the input is from the Sonos app in the first place, and volume control. And it's useful that the Sonos volume drops when Alexa hears "Alexa", so you're no longer shouting at the Echo over the Sonos volume.
I saw this at https://sonos.custhelp.com/app/answers/detail/a_id/4343 :-
"Spotify users: We’ve heard from you and are working hard to bring you the ability to ask Alexa to play Spotify music on your Sonos speakers as quickly as we can."
Please add Deezer to that? And local libraries? What we have is next to useless to anyone not using Amazon Music.
I was expecting full control of Sonos over Alexa. What we currently have (and I know it's in Beta, which is why I tagged this as feedback) is a crippled, glorified Bluetooth speaker.