EDIT: Well on a re-read of OP, this more or less completely fails the "simple" aspect. Leaving this here just because it is really fun to do this kind of thing anyway!
If you're into building things and technology, something like raspberry pi + microphone can easily handle the business (computer) end of Sonos for like $20, especially if it isn't multi-room. It'll also likely take 5 times as long to get up and running as just buying something if you've never done this before and you may need to do troubleshooting once it's operational. From there you just need a receiver, some speakers, and some cord.
I did it this way because I like that kind of thing and it isn't really that hard, and I wanted to have separate computer, speaker, receiver, amplifier pieces so I could swap them out and use them for other things e.g. a record player. I also have grand fun plans for other functions the Pi can serve at the same time as being the music computer (e.g. it could be the brains of a remotely-operated door lock, motion sensing camera, "smart" mirror). But then I also built my speakers from scratch and will eventually build a receiver, amplifier, and sub too so I'm not exactly normal! I'll likely add a second set and do synced multi-room when I find the time.
If occasional troubleshooting via googling and updating some simple code occasionally doesn't sound like a good time I'd look another direction. Same if it's something you need to "just work" for anyone who wants to use it for 5-10 years.
I appreciate the thoughts, but yea, probably too complicated. The DIY rabbit hole can be as deep as you want it to be (and I've never even heard of people building their own speakers!), but at this point in my life I have to pick and choose hobbies. For the same reason, I abandoned home brewing. (As a chemist, I love brewing, but homebrew is way too time consuming esp if you do all grain... this contrasted by the cheap price of good beer nowadays, makes it not worth it). For this reason, I might consider it in retirement, but not now.
In addition, I'm a proponent of the general mustachian efficiency theory, which is to DIY it just enough to get maximum benefit versus effort expenditure. Eventually you hit diminishing returns, which are only worth it if you are super interested. I am interested in learning more, but at this time I only have so much free time.
I am probably going to try to learn a bit about speakers and head down the audiophile rabbit hole, but not balls deep, just the tip. Therefore, I might consider getting some separate speakers connected to an amp, but where do I stop? Do I get a subwoofer? Do I look into sound dynamics to fully optimize the listening experience?
In the end, I need to learn more to better quantify my objectives, but I can at least say the basic qualitative goals:
-good sound quality, but doesn't have to be perfect
-cost <$500 for now; upgradability might be nice
-wifi control is a must
-direct voice control is not a must, but I should at least be able to connect it to Alexa (or similar).
-for now, I'd like to set an upper limit to 1-2 months of research time. Setting up the holy grail sound system can occur later in life (if ever)
Anyways, I've probably made this an overly complicated post at this point, but it anyone has gone down this rabbit hole before and can send tips or recommended reading/learning materials, I'll take a look.
In regards to writing code, and using Raspberry pi (which mostly just sounds delicious), I know very little about code. It's a skill set I'd like to eventually develop, but probably a bit much for now (unless it's really not that hard to learn from scratch).
