For Raspberry Pi and Tidal I use Volumio on the Pi and Bubble UPNP to send Tidal to it (it can also do the same with your plex library). The full version costs a couple of quid but works nicely to send a whole variety of stuff to a whole variety of other stuff.
An android. Currently I can cast to my TV but that doesn't do gapless.
Im looking for a way to do what Roon does with paying roon cash. Mostly streaming tidal to be honest.