Need Recommendation for Wi-Fi capable Receiver for Pool Speakers

A lot to unpack here. I assume the 3 speakers are still there? If so, unless they are wired in a strange way, I wouldn't run 3 speakers. I would only run two, optimally the two that are the furthers apart unless one is ridiculously far away from the pool area. That way you are using a two channel amp and things are much less complicated.

If it were me, I would be worried about strange impendences messing up my new receiver. So you'll need test the speakers back at where they terminate. You'll need a multi meter for this. It's a little involved, but worth it. (All of this assumes the wires aren't labeled) First, disconnect all of the speakers from the speaker wire. Then twist the two ends of one of the speaker wires together. Go back to the speaker wire termination location and test for continuity. Find the two speakers you want to use and reconnect them. Google how to test speaker impedance and follow the directions using your multi meter. Make sure that the readings are roughly the same and that range is within what your amplifier can handle. At that point you have the speakers sorted out.

For step two, Find a receiver that has Spotify connect and you should be good to go in that regard. You could also use the outputs from a dedicated Alexa device (or similar) to control music the same way.

Sonos amp supports 4 speakers. Just do that and call it a day.

I had a similar situation at my current house. Speakers everywhere. What works for me is basically any receiver plus a streamer and an impedance matching speaker selector. I tried using just my Onkyo with Chromecast built in, but it was slow and glitchy. My Wiim Pro has been awesome, as was my original Chromecast Audio. I now have only the kitchen and 4 patio speakers activated as those spaces turned out to be the only ones we really want music at. The kitchen has a volume control, and each pair of patios has its own. If I was not clear, please ask for any clarifications.

I wish I would have done something like this. I ran an Onkyo with a Zone 2 from my tv room outside to my pool area so I could power 2 speakers and send my Comcast tv signal to the outside TV. This was a ton of effort, glitchy, locked up, had to reset the onkyo all the time. I moved to YOUTUBE TV and now the outside tv just uses the app & wifi and my two powered speakers are basically useless.

I can still push music out there from the Onkyo if I want to go the trouble but that wasn't worth the headache and expense of setting it all up.

You have work to do:
1. Send pics of speakers or determine impedance and number of coils.
2. If SVC, hopefully they are 8 ohm and you can easily used bridge outputs on a multi zone amplifier.
3. If DVC, each speaker is a zone. L+R channels.
4. Determine interface. Juke dominates modern conversion setups. AirPlay 2 allows for multiple WiFi receivers to sync as zones and you can group them. You’d just attach wimm pucks to an old 12 channel amp that is nearly free second hand. Only need one puck per zone that you want to group, so just one if you don’t have indoor speakers also.
5. See if it might be easier for you to ditch the speakers and go with Sonos or something easier to manage but with more crap software between you and your speakers.
6. DVC could also allow wiring as S+P and use a single wimm amp or similar.

I use a Yamaha two zone receiver that has solid internet radio and streaming services, and my zone 2 are my outdoor wired speakers by the pool. I control the pool speakers using my phone. It is a seamless app. The Yamaha is also connected to my main TV and runs a 7 speaker setup in that room. Each zone can be separately controlled so that we have TV sound in the main room and streaming music by the pool.

But that is not unique to Yamaha. All I can offer is that the Yamaha AV receivers do a really good job in a set up like the one you describe.