If you have the latest Apple TV Siri Remote (the one with the Mute button) and a Sonos Playbase speaker, you may find that Mute doesn’t work. Briefly, the solution is to set the Apple TV to use the Playbase as an AirPlay speaker. If you use the Playbase as a wired speaker, depending on your TV, the Mute might not be a permitted action. (I have a Sony Bravia TV, which treats the Playbase as an external audio system with immutable volume settings.) Switch to AirPlay, though, and all is well.