This is the way. Edgerouter-X is basically free for the price. You can then go figure out your wireless strategy seperately.

They’re kinda shitty? I think the Maxs are better - but its usual consumer audio ‘ooh what a great bass’ kinda crap.

Soon^tm you’ll probably be in a situation where off-the-shelf flexible smart speakers for local hass are more common.

It will link to the chromecast in as much as you can add the TV to a group and play something to a whole group of speakers.