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Like how do you listen to high def formats that are becoming more accessible. Ie

Tidal, Amazon music, etc

It seems to me, these are mostly headphone-consumed formats.

I listen to Tidal or my own streamed DSP/high def music via a variety of speakers, never headphones. Oppo, Roon (both for Tidal MQA), Heos directly to receiver. The options for ways to play keep increasing.
 
I had a stereo pair with the ATV as a "home cinema" solution. I got rid of them, it was painful. First of all only ATV content works with them so normal broadcast TV wouldn't and neither would apps on the TV itself (although that part isn't really a problem as the apps can be installed on the ATV)
This would be a sticking point for me as well. I have an A/V receiver which takes in HDMI connections from my ATV, PlayStation, blu-ray player and a TV tuner -- and outputs the audio to a pair of good speakers and the video to a projector.

When I got my HomePod a couple weeks ago, I was very impressed with the sound, and briefly considered getting a second to do what the OP is suggesting. But as you say, only the ATV would be able to access the HomePods for audio, unless maybe I got some kind of AirPlay compatible A/V receiver (?) And even then I'm not sure it would work, and issues of latency and wireless stability would be introduced. For me all the money and time would probably be better spent upgrading my projector to 4K.
 
An Airplay receiver would be the endpoint, you can’t use an Airplay receiver to send sound to Homepods. You can only send sound to the receiver via Airplay to be played via wired speakers.
 
To me sound is also somewhat important. I use a late 2013 iMac in my home office solely for the purpose of playing music from my library and iTunes. I use a set of Klipsch powered book shelf speakers and a Klipsch 10" powered sub. The Klipsch combo cost less (at the time) than a pair of home pods.
 
There are a lot of elements to sound "quality". In the lab, or in a controlled setup like a dedicated listening space, I'd choose dedicated, traditional speakers over the HomePod. I think the feature most overlooked in HomePod is the implementation of 360-degree sound and spatial awareness. Even great speakers can be ruined by a poor listening environment. My Focal CMS 40s sound much, much better than my HomePod in my treated work space where they are carefully aligned to my usual sitting position; however, I'd much rather have my HomePod in my open living room/kitchen/dining room where I'm moving around making dinner while my daughter has an impromptu dance party while procrastinating her homework.

Life happens on the move. That's where the HomePod excels. There is no critical listening spot with HomePod and that's by design. Kills me that so many reviewers of the HomePod plunked one down next to their dedicated hi-fi, sat in their well-worn listening chair and said, "yeah, it sounds good/bad/the same as XXX". Of course some (fewer IIRC) reviewers did similar things with the AirPods Pro by comparing them to comparably priced *wired* headphones. Luckily most consumers instinctively realized the incongruity of that comparison but most consumers have limited/poor experience with home audio and didn't understand the value.

That beam forming also works great for Atmos and home cinema is a happy by-product. I'm cautiously optimistic that Apple will resurrect the HomePod and apply this tech to the home cinema space where, ironically given that cinema is almost always consumed sitting in the same space, the advantages of spatially aware speakers is better understood. The TV/home cinema also seems to be where most Americans (anecdotal, even less sure outside the USA) consume "serious" audio outside of their cars. Because of poor quality PA systems, badly reproduced recorded music is the background noise of our lives. High quality music playback is unexpected and almost odd. Movie theaters have kept consumers expectations for cinema audio high.

/rant
 
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