Output of Apple TV 4K

Apple TV 4K can output audio to a set of wireless speakers, instead of built-in TV speakers, or instead of TV-connected speakers (e.g. soundbar), or instead of HDMI connected audio system. One audio output can be used, except for audio-only sources (mainly music) in combination with AirPlay 2.

• HomePods can be configured as default audio system for Apple TV 4K. (See Rudegar’s reply.)
• Other AirPlay-compatible speakers can be a temporary audio output (i.e. re-select each time you want to use it).
• Bluetooth speakers can be a temporary audio output as well, including wireless headphones.

Add different speakers through Apple TV Control Center - Apple Support

Use Bluetooth accessories with your Apple TV - Apple Support

Wireless speakers must be AirPlay-compatible from the manufacturer to be able to be used with AirPlay.

Use AirPlay to stream audio - Apple Support

AirPlay system requirements - Apple Support

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Set up home theater audio with HomePod mini or HomePod and Apple TV 4K - Apple Support