AVB is an audio networking protocol utilized by PreSonus audio hardware. It is similar to Dante, whereby all of your audio data is transmitted and received via ethernet cables rather than bulky copper audio cables.
This article talks about how to ensure that your Mac running OSX will be able to send and receive audio on the AVB network.
It all boils down to an automation that plays media using Spotify as the source when triggered. In this case, the trigger will be the state of our digital shower valve which is a simple on/off switch. The media player will be a PiCore Player (squeezebox) running on a Raspberry Pi3b, and the media source (i.e. the song played) will be a link to a Spotify track (URI).
The concept is simple. Create a group of buttons of which only one can be active at any time.