Hey guys,

I read many similar topics, but none had a solution that worked on my setup.

Setup / Environment

Devices:

• Audio System (named as “Living Room” in the Sonos app)
  • Sonos Arc
  • Sonos Sub (Gen 3)
  • 2 Sonos Era 100 (Rear placed)
• Sony A95L TV
• Apple TV 4K

Connectivity:

• Apple TV is connected to the TV on a HDMI 2.1 (CEC) port with an HDMI 2.1 cable
• Sonos Arc is connected to the TV on a HDMI 2.1 (CEC, eARC/ARC) port with the Sonos Arc’s provided cable

Configuration / Settings:

• Sony A95L TV
  • Picture & Sound
    • Sound (Audio system)
      • Dolby AC-4 Dialog level: Min
      • Dynamic range: Compressed
      • DTS Dynamic range: Disabled
    • Prioritize HDMI signal information: Enabled
  • Audio output
    • Audio system settings
      • Acoustic Center Sync: Disabled
      • Audio system prioritization: Enabled
      • A/V sync: Auto
      • Digital audio output: Prioritize passthrough
      • eArc setting: Auto
      • Optical digital audio output volume: Max
• Apple TV 4K
  • Video and Audio
    • Audio Format
      • Change Format: Off
      • Dolby Atmos: On
    • Audio Mode: Auto
  • Remote and Devices
    • Control TVs and Receivers: On
    • Volume Control: Auto via HDMI (Receiver)
• Sonos
  • “Living Room” Settings
    • Surround Audio
      • Surrounds: Enabled
      • TV Level: 0
      • Music Level: 0
      • Music Playback: Full
    • Sub Audio
      • Sub: Enabled
      • Sub Level: 0
    • Height Audio
      • Height Level: 0
    • Volume Limit: Off
    • Spatial Music: Enabled
    • TV Autoplay: Enabled
    • Ungroup on Autoplay: Enabled
  • Audio Compression: Automatic

Problem

When I play stereo music or a YouTube video on my Apple TV, my two Era 100 speakers output almost no sound. It’s as if only the Arc and the Sub was outputting sound. When this occurs, I see in the Sonos app that my audio system is receiving “Stereo PCM”. I want the Era 100 speakers to also output sound such that I feel the audio coming from both the front and back.

If I make the Apple TV output its audio to the audio system through Airplay (instead of HDMI), the problem doesn’t occur. However, Airplay isn’t compatible with Dolby Atmos so it isn’t viable for me to always use Airplay over HDMI.

When I play Dolby Atmos content (music or movies) all speakers are well used and I can see “Dolby Atmos” appearing on the Sonos app. 

When I play a 5.1 Netflix movie, all speakers are well used and I can see “Multichannel PCM 7.1” appearing on the Sonos app.

Disabling the “eArc setting” on my TV seems to fix the issue, however, as far as I understand, I wouldn’t be able to get “Dolby Atmos MAT” anymore and would be stuck with “Dolby Atmos DD” which is lower in quality. I don’t want to sacrifice the quality of Dolby Atmos content.