That's because it's not supported.
If you have both of these questions, buy a soundbar instead of HomePod
"Can I set up a stereo pair?"
"Can I use the stereo pair on a TV?"
The other reason it’s different from AirPods is that, I believe, AirPods connect over Bluetooth, not airplay.
From what I read, Apple TV can also output audio to airplay speakers, but up until now it could only connect to one speaker at a time, and I’m not sure if that works for movie audio as well or only for music. With airplay 2 I understand that it will be able output to multiple speakers, but again I’m not sure if that includes movie audio, and the bigger question I’d say is whether or not it can do multiple speakers with separate stereo channels. Probably not, I would guess right now with my feeble understanding.
I’m actually leaning toward neither HomePod nor sound bar, but a stereo receiver and speakers (hooked up to my Apple TV), which I could then control with the remote or another Apple device. But I haven’t done much research yet so I don’t have thorough knowledge of my options. I will have to hear the sound quality of the HomePod for myself before making a decision. I doubt the sound quality of two homepods can compete with a receiver+speaker system I can get for around the same price (or perhaps I’d want something better for more money), but if it somehow does, I’ll have to re-evaluate, taking into account the extra Siri functionality, which I would find useful. Siri would make it easier to start listening right away, rather than having to first find my nearest Apple device (and possibly having to turn on the receiver?). And I would welcome being able to talk and listen to Siri normally instead of yelling and straining to hear when my phone is across the room. Siri also works better for me than other assistants because of the Apple ecosystem integration, for things like adding to my reminders and lists.
Anyway, we’ll see soon enough.
Edit- actually I already have a sound bar but it doesn’t give me the quality and stereo separation I want.
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I do have a sound bar, but I’m just interested in If it will work. I already have my end all be all, but I/we just are speculating.
I’m just saying that here isn’t any reason why the Apple TV shouldn’t connect. One, for sure, at launch. Two, with stereo via airplay 2.
Yeah I would be very surprised if at least one didn’t connect, and at least for music.