Best answer by Ryan S
You can use Alexa to start playing from Amazon Music, Amazon Music Unlimited, Pandora, iHeartRadio, SiriusXM, TuneIn Radio, and we’re working to bring Spotify controls in the future too. Alexa doesn't have access to your local music library.
Also, any Alexa device on your account can use basic controls, such as play, pause, volume, and skip, on your Sonos players. This works for all services and music on Sonos, started through the Sonos app.
We don't have any specifics on what's up next, or if local library will be working for the future, but the skill will be improving over time, so you never know what might get added next.