Change default sound output on Apple TV 4K: *not* TV Speakers

Fair enough, @The Customer. I respect your anonymous tendencies, your taste in audio equipment, and your aversion to hacks! HomePod minis indeed… :-).

Although, settling for an AirPlay 2 link between your audio source and speakers seems like a bit of a hack in itself. Too bad the Bluesound NODE doesn’t support WiSA connections direct to your speakers - have you looked the WiSA SoundSend? Anyway, my knowledge of high end audio is just curiosity-driven Internet superficial, so, no need to respond.

FWIW, if you use an iPhone (which seems likely since you have an Apple TV 4K), you have the ingredients for setting up the HomeKit Scene I described without enabling any microphones to be constantly eavesdropping while on the alert for “Hey Siri” commands. Your ATV4K would serve as the HomeKit hub while your iPhone can be used to configure the described Scene using the Apple Home app and then to issue the discreet Siri command with a long-press of the power button.

BluSound Node

Which has HDMI-in (“HDMI eARC”). Please use it. It’s even better than AirPlay.

‘TV Speakers’ is a bit of a misnomer, as it is used for audio-over-HDMI, even if the TV is not the audio destination. Set your TV for audio passthrough. Apple TV →[HDMI]→ TV →[HDMI (e)ARC]→ audio system.

Apple TV keeps defaulting to "TV Speakers" as the default for sound.

Is there a way to set Airplay as the default sound output?

With current software, AirPlay or Bluetooth speakers are always a temporary audio setting, unless HomePods.

It sounds like you didn’t buy into Bluesound’s wireless speakers yet or you would simply place the NODE by the ATV4K & projector and configure it to play to the pulse soundbar, etc. under the screen… So here’re a couple of suggestions/hacks.

For a cheap/easy fix, you might consider and be surprised by the sound produced by a pair of HomePod minis… at $99 each, the pair will cost less than half of what you paid for the ‘NODE. I happen to use an Atmos-capable HDMI-connected soundbar for watching TV, but I have a pair of HomePod minis in the adjacent room… when I tried them out as a “soundbar alternative”, using the default audio output feature, I was pretty impressed! So was this home theater ‘blogger guy.

Before you spend any more cash though (here comes the hack), try creating a HomeKit scene to mitigate the hassle of manually connecting the NODE via AirPlay each time you’re watching the Apple TV. I believe you could add the NODE and Apple TV 4K to your HomeKit setup as accessories, then try creating a scene, call it “Home theater”, that includes both. You can play with supplemental settings details in the scene. Henceforth, a “Hey Siri - Home theater” should wake up the ATV4K and link the NODE via AirPlay.

I don’t have any stand-alone AirPlay speaker accessories in my HomeKit setup to test what I just suggested, but I often want to have the HomePods playing a Pandora station while also hearing it through the ATV4K-connected soundbar… This was a two-Hey Siri command sequence: “Play station”, then “Also play this on Apple-TV”. I created a “Music everywhere” Scene that does join the HomePods and ATV4K via AirPlay and resumes what was last playing on the HomePods. If I used an Apple Music subscription (instead of the Pandora stations I’ve tuned over the last 12 years) I could also specify a particular music selection, but that’s me running into the non-Apple product penalty akin to your default NODE challenge :-).

I did make a product request of Apple to let HomeKit scenes execute typed Siri commands, but that hasn’t happened so far.

[edit: too slow sitting idle in edit mode - redundant after @Urquhart1244’s spot-on-answer]

I’m afraid not - AirPlay speakers can’t be configured as the Apple TV 4K’s default audio output. At this time, the only option aside from the HDMI connection are HomePods (original or HomePod minis in the same HomeKit Room).

I gather the Bluesound Node can be hooked up to your TV’s [e]ARC output, so that’s probably your best option.