Dolby Atmos over Airplay with Third Party speaker doesn’t work with iOS 18.2

I have a Devialet Dione (Firmware 2.16.1) and a house full of Apple Devices. I have tried playing Atmos content from Apple Music via Airplay on the Dione, but it only plays in Stereo. When I launch the song on the Apple TV 4K that is connected to the Dione via HDMi, both devices confirm they are playing in Atmos and it does very audibly so, it sounds incredibly well. I also have to HomePods Gen 2 and can confirm they play Atmos over AirPlay. Apple said that Dolby Atmos over AirPlay 2 would work in iOS 18 with Third Party Speakers, but without any details. Did someone get Atmos over AirPlay to work? What are supported devices, if any? I have an iPhone 15 Max running iOS 18.2 and the Apple TV 4K as well.