We’ve teamed up with Sonos to make it easier than ever to keep the music going strong. Now Spotify Premium users can control their Sonos straight from the Spotify app using Spotify Connect. Use all the features you love about Spotify: the curation, discovery, and sharing and hear it all throughout your home in crystal clear sound. You can also access the multiroom power of the Sonos home sound system directly in the Spotify app. We’ve brought out the best of both worlds to give you the smartest and most seamless home sound system yet.
I've been trying this in beta for the past couple of months, and it has worked well with my Sonos PLAY:1. The feature is based on Spotify Connect, which is fast and doesn't route all system audio to a single device. In my experience, using Spotify Connect with a Sonos speaker has been much more reliable than streaming music to AirPlay or Bluetooth speakers.