Streaming from the Apple TV to the Belkin basically works without any problems. However, there are 2 things to note:
- Multiroom streaming with the Spotify app does not work (Spotify on the Apple TV can currently only do AirPlay 1, so either only Belkin or only Apple TV, but not HDMI + AirPlay at the same time, for example).
- The setup requires an iPhone/iPad. There is no other way, as the Soundform must be installed via the HomeKit function. Otherwise you can't even get it into the Wi-Fi network.

Lukas, setting up 5 Belkin Soundforms worked perfectly for me. They supply various sound systems in the house.
The Apple TV 4K can also be set up so that individual or all Belkin Soundforms including sound are controlled via the TV.

Go to Settings Apple TV 4K--->Video and Audio--->Audio Output--->Temporary Audio Output-->here you select the sound output and the volume.

Ruedi