You can setup 2 Homepods and pair them together for true Stereo sound with an Apple TV
But can you setup multiple homepod pairs for extending this stereo sound?
Such as 4 homepods == 2 pairs
or even 4 homepods and 2 homepod minis == 3 pairs ?
On iOS 14.3 and tvOS 14.3 on Apple TV 4K you can only add one or one paired set at a time in the default audio setting on an Apple TV 4k for the “Home Theater” mode. Once you’ve applied that setting on the Apple TV 4K you will override the AirPlay function in control Center and cannot remove any you added . Set up home theater audio with HomePod and Apple TV 4K - Apple Support
If you want to play to more than one HomePod or more than one pair, it’s best not to use that setting - so set that to tv speakers in ATV Settings > Video and Audio > Default Audio Output. Then you can go ahead and AirPlay to as many as you like using control Center like this:
to bring up Control Center. 
.I’m not sure how the default audio setting works on Apple TV HD (if it overrides control Center)
Or you can use the swipe down method to AUDIO to make your selection
Until such time they issue a software update to fix this, this is how it now is.
I hope that explains it.
On iOS 14.3 and tvOS 14.3 on Apple TV 4K you can only add one or one paired set at a time in the default audio setting on an Apple TV 4k for the “Home Theater” mode. Once you’ve applied that setting on the Apple TV 4K you will override the AirPlay function in control Center and cannot remove any you added . Set up home theater audio with HomePod and Apple TV 4K - Apple Support
If you want to play to more than one HomePod or more than one pair, it’s best not to use that setting - so set that to tv speakers in ATV Settings > Video and Audio > Default Audio Output. Then you can go ahead and AirPlay to as many as you like using control Center like this:
to bring up Control Center. .I’m not sure how the default audio setting works on Apple TV HD (if it overrides control Center)
Or you can use the swipe down method to AUDIO to make your selection
Until such time they issue a software update to fix this, this is how it now is.
I hope that explains it.
I wanted to add that in any situation where you AirPlay to more than one home pod in iOS 14.3, they get stuck merged and when you go to use them next time you are not able to unlink them. If you want to play music to just HomePods it will turn on your Apple TV ( if that was included in your last used) If you want to use just one HomePod for an audiobook it will play to everything that you used last. Like if you used all rooms for music. It depends on how you like to use them . So just keep that in mind if you’re playing to all. I could probably have written my above post better but it was too late to edit.
Homepod stereo pairing
