I have the beam and a HomePod.
because I have sonos around the house, I don't normally use the HomePod for music, just for "hey siri" control of homekit.
(I bought the HomePod before I went sonos, probably wouldn't buy it now)
I do live in an apartment, so am a bit conscious about making too much noise or bass.
The beam sounds great, it doesn't have that tight thumpy bass that the HomePod does though. it's got some bass, but won't rattle the room.
I do have the sonos sub, with that the sound is pretty comparable. I normally keep mine turned down some, but that's due to being in an apartment.
When comparing the cost of the 2 systems "1 Beam + 1 Sub = 5 HomePod"
I'm amazed at how "wide" it sounds, (the bar is 2' wide, my tv is 4') and when playing channel test tracks, it sounds like the speaker is beside the TV.
with the beam you can also add a sub or surrounds (you can get the cheapest speakers for the surrounds, as the voice assistant options aren't available when the speakers are used as surrounds. You also don't need to worry about the surrounds not supporting airplay on their own, as both of the features are handled by the beam)
The sonos in my bedroom have airplay, and I still use the not so great speakers on the TV instead of airplaying from the aTV.
from my experience and what others have said on here, using HomePod as main speaker for the aTV isn't the smoothest, as it keeps unselecting itself, and can cause delays when starting playback. You get none of this with beam, since it's connected directly.
I'm also much happier with the process of music playback on the beam. the whole process of airplaying to the HomePod was a bit kludgy for me. with sonos, you can just choose songs and playback from their app. And from any streaming service. (can even make a mixed playlist of the different services if you can't find music you like on one or the other) And at least for Spotify it supports multiple accounts, So you and the wife can access both your playlists.
Sonos has apps for iOS, android, and computer. You can control the whole system from any of them. So if you start playback from your phone, your wife can add songs to that playlist from her computer. And you can join/unjoin speakers from the playback group using any of the apps also.
One thing, they've limited the computer apps, So those are only good for playback and EQ adjustment. All Setup and configuration happens only on your mobile devices (but you really only need that when you add new speakers)
Your phone's microphone is also used to EQ the speakers to your room and adjust timing of surround speakers. (also normally only done at initial setup) HomePod does this automatically, and seems to do a pretty good job of it.
I don't really use voice assistant to start play music. so can't comment on that.
since you've got HomePods everywhere, this won't apply as much to you, but once audio is in the sonos system you can play it anywhere, I can see my TV from the kitchen, so I add the kitchen speaker when I'm working in there.
as far as airplay and sonos...
as long as one of your speakers supports it, the rest of the speakers in the Sonos system can grab the audio using sonos protocol.
Sonos is only an airplay target. So HomePod to sonos will work. Sonos to HomePod won't
another nice sonos feature is doing a long press on the built in button will join that speaker to others that are already playing, no grabbing phones or anything.
