Stereo only wireless "surround sound" set-up

Looking for help to commit sacrilege.
I’m trying to figure out a way to keep the Naim Mu-so 2 I already own as a “soundbar” and get two rear speakers for some more stereo oomph behind me to have a “surround-sound”-esque set-up for movies. The problem is figuring out how to do it all wirelessly. I’m ok linking up the Mu-so 2 via arc to the TV but is there a way I can have my cake and eat it too?

Mucking around with Chromecast has revealed the option to add speakers and even smart TVs to a broader speaker group for multi-room audio. Do any boffins here know how I can use a chromecast multi-room set-up to be able to play TV audio? I recognise the simplest solution would’ve been to stick to Sonos but I really dislike closed ecosystems and feel like a lot of “surround-sound” is gimmicky.

All best,
W.