I’ve got a small squeeze box system up and running. I had built a house wired for in ceiling speakers in every room and was starting to build out a system, then we decided to move. I can just imagine a rack of pis sitting in the wiring closet running the whole house. Oh well…
I have a Linux server running Logitech media server on docker. It works flawlessly. I think it has pretty low resource requirements. Since you already have a Linux server I would definitely recommend installing it there either directly or in vm or container.
I have one pi3 with a hifiberry amp+. It has picore player installed on it. I remember when I was first setting it up that I had a hard time finding a tutorial for exactly that setup and tried a number of different options that I couldn’t get to work for various reasons. Picore player, once installed, has an option for hifiberry in its web interface and couldn’t be easier to configure. You could use other distros, but if squeezebox is the only thing you’re using a particular pi for, you can’t beat pi core player.
I just checked the hifiberry website and it looks like they have an amp2 product that is better for the same price as amp+. Probably should go for that one if you haven’t purchased yet.
I have a second pi3 running picore player. This one is connected directly to a cheap $10 set of USB speakers. This works great just like the first one. Since the USB speakers have the DAC chips, there was no need for hifiberry and it was a lot cheaper.
Back when I had the house wired for whole house sound, the hifiberry looked like the best option, although I remember it looking like it would be $100+ per room so I was just going to gradually build out the system. Thr rooms just had wiring, no speakers, so I had to purchase a speaker when wiring a room. Monoprice had a decent inexpensive speaker that I was going with. I think if some rooms just have one speaker, it’s theoretically possible to use a single pi with hifiberry amp+ to run two rooms using the left and right channels separately for two instances of squeeze lite, but I didn’t have enough pulse audio configuration skills to make that happen. That could bring the per room price down. I’d recommend considering the USB speaker route if a room isn’t already wired with speaker wire and you want to add a whole house speaker.
I have plex but never really used it for internet radio or local music. If you already use it for that, Logitech media server might have a plugin to connect. If you don’t already use it, I would recommend just going through Logitech media server/squeezebox.
I use an android app called squeezer to control swueezebox. It works well.
I don’t do much with the audio in openhab as far as selecting sources. We’re primarily using it as white noise for our two babies. When either of their bedroom doors close, a single white house track is started on repeat and the volume is set to the proper level. When the door opens, the sound turns off. Works flawlessly.
Hope that helps!