You need to send a Dolby Digital 5.1 signal to the Beam from the tv. The system doesn’t just make up some sounds for you. 

I know...I have apple tv 

And it's on 5.1 Dolby Digital 

And still don't working...

Get a DD signal playing. Then, in the app, go to Settings, System, About my System. What does it say  for Audio In for the Beam?

So sorry but I didn't understand you..

“ Then, in the app” in what app..?

How are you controlling your Sonos system? I’m assuming - which may be stupid of me - that you’ve got the Sonos S2 controller application running on your phone? If not, how are you streaming music to it?

I have sonos arc…

And it say stereo pcm 2.0

So the Arc is not receiving a DD 5.1 signal; only 2-channel. If you are sure the program you are watching is being transmitted in DD - many are only stereo/2-channel - the tv settings need to be changed. The Arc can only play what’s sent to it. 

Thank you very much for your reply.

I'm watching on Apple TV the Netflix app 

5.1 DD