Best answer by yayarod
to allow that your setup works as you expect yo need to connect both the Apple TV and the SONOS Beam each with one cable to the TV.
To only hear music you can use the SONOS app with your selected services or use AirPlay from your iOS device.
With this setup if you AirPlay a video to the Apple TV it will sound through your SONOS system since it’s cable connected to your TV.
As I wrote earlier in this thread, you only can select the audio output on the Apple TV if it is the source of the media, if you are using AirPlay on it, audio defaults to the HDMI output, but since the Beam would be cabled to your TV you would get sound through them.
You will need to connect the Beam to an HDMI ARC port on your TV and the Apple TV to a regular one.
Hope this helps!