Owntone does Spotify premium accounts and serves up a web page you can use to control it. Itunes remote app as provided by Apple or "Retune" app on droid also w

Owntone does Spotify premium accounts and serves up a web page you can use to control it. Itunes remote app as provided by Apple or "Retune" app on droid also work to control. Any additional airplay speakers (or shairport-sync) can control to have the sound coming out of them aka multiroom. Owntone integrates nicely with home assistant if you want to go there too. If you can run a light webpage with the tablet it should be enough. Owntone and homeassistant need to run somewhere else on your network like on a pi, or an old laptop. Your app only heating controls may well also integrate with homeassistant, a hell of a lot of that kind of stuff does. Homeassistant also serves up a light web page as a control interface. There's phone & tablet apps too. Worth a look, imho.