Assuming the A4A will be in Pure Direct mode for Stereo playback of the signals coming in from the DAC as
@Eppie mentioned, the Apple TV 4K would need to be connected directly to a TV and it connected to the DAC via optical.
If the connected TV supports eARC, multichannel PCM signals from the Apple TV 4K will be available to the A4A via HDMI eARC when settings are changed back from Stereo. The TV’s digital audio output setting should be set to Passthrough.