Only Stereo output from Apple Music/TV

[eiriasemrys]

Hey guys, wondering if anyone can help me here? I have upgraded from Big Sur to Ventura and now I lost the ability to play Dolby Atmos and/or 5.1 from Apple apps through my audio interface. Only Left and Right Channels seem to receive streams from Apple Music, Quicktime, and Apple TV.

I have a Scarlett 18i20 with a 5.1 JBL Studio speaker setup.

What works:
- PC games that use surround, with the 18i20 set as the output device (also works with virtual surround devices using Loopback)
- Professional apps, with the 18i20 set as the output device (also works with virtual surround devices using Loopback)

What doesn't work:
- Apple Music Dolby Atmos Playback
- Quicktime 5.1 or Atmos Playback
- Apple TV 5.1 or Atmos Playback

The Setup:
Scarlett 18i20 > Audio MIDI Setup > 5.1/5.1.2 Dolby Atmos
ALSO:
Virtual Loopback Audio Device > Audio MIDI Setup > 5.1/5.1.2 Dolby Atmos

What I have tried:
- Reinstalled the AppleALC kext, update, etc.
- Uninstall Loopback and ACE
- The same setup on a M1 Mac mini to verify that these apps in Ventura should still see the Scarlett 18i20 as a Dolby Atmos capable system, verified working.

Here's a screen of the virtual device that just illustrates the issue during playback of an Apple Music Dolby Atmos song:

 

[eiriasemrys]

And this might be helpful here, if I DISABLE AC3 passthrough in the Apple TV player, surround/atmos works. Time to do some digging on AC3

 

[eiriasemrys]

Okay I finally solved this and wanted to followup for future folks with the same problem.

If you are using Loopback on Monterey and Above, you MUST create a virtual audio device with 16 channels, even if your setup is actually 6 channels (5.1) or similar.

Secondly I had to set Apple Music to Automatic for Dolby Atmos Playback, "Always" was intermittently successful.

Lastly, before trying Apple Music again, with it closed, delete /Users/resolve/Library/Caches/com.apple.Music/fsCachedData