What specific apps are you using? Are you using the TV’s internal apps or apps from an external media device? What model TV do you have? Can you post photos of your current TV audio settings?

I’m using an Apple TV 4k as a source to a Sony Bravia x90J TV. I’ve played around with the Sony TV’s settings (currently set to passthrough). If I disable eARC on the TV all the sound to the Sonos is normal. It passes Atomos, Dobly Digital and Dolby Digital + correctly. If I set TV to eARC, Atmos works, but everything else is passed as PCM - PCM 2.0, PCM 5.1 multichannel, etc. But the volume for PCM is waaaaaaaaaaaaaay too low and the surround effect are almost no existent. 

The Apple TV 4K uses Dolby MAT to play Dolby Atmos audio. Dolby MAT requires eARC so it should be enabled on the TV. Because the Apple TV uses Dolby MAT, all non-Dolby Atmos audio will play as Stereo PCM or Multichannel PCM out of the Beam (Gen 2) unless you set the Apple TV Change Format option to On and set the format to Dolby Digital.

Try these settings on the TV:

Speakers - Audio System
Auto System Prioritization - On
A/V Sync - On
eARC - Auto
Digital Audio Out - Auto 1
Digital Audio Out Volume - Max
Dolby Digital Plus Output - Dolby Digital Plus
Pass Through Mode - Auto

Yes. Thank you! I understand all that. And those are the settings I have tried on the Sony TV -- and those settings on the Apple TV. The issue is there is a noticeable, and significant difference in sound volume and quality! of sound, between using the eARC setting (which passes everything as PCM) and using just plain ARC (non eARC). Using ARC (not eARC) results in a significant difference (and better) sound versus eARC. Something is off with how the Sonos Beam handles LPCM. Looking through the support discussions, this seems to be a known issue -- I.E., how Sonos handles LPCM streams. 

Hi, is there any update to this situation? 
I am facing the same situation when i activate the eARC mode on the TV (X90J) then the content is on PCM unless it s Atmos (I am mostly using AppleTV 4K). 
And yes the sound is very low and sounds better when it is not activated… 

Is it some bug? 
 

Thanks,

actually even when the eARC is off, I am getting Dolby Atmos. Do you think there is difference in the quality when it is ON for the Atmos?

Only you can judge the quality of the sound you are hearing. What do you think?

The volume is def lower but this happens actually only with Apple TV.