Can you do something like say "play <songname> only in the living room and the kitchen" and have it play something completely different in the other two rooms? Assuming that Spotify lets you stream multiple songs concurrently, that is.
On the sound quality tangent, I used to have a well reviewed Cambridge Audio soundbar thingy which included 2" tweeters and 6.5" woofers. I got bored and ended up building a cheap DIY bookshelf speaker kit and ran them through a cheapo bluetooth amp. And realised that the soundbar which I thought was good, was murky garbage. I would not call myself that picky with sound, but I've recently become aware that 'convenience' consumer audio products are highly, highly compromised.