remotely setting a Mac's audio output device

I have a dedicated Mac ("retsina") for serving media. It's cabled to my router, as is my gen 4 Apple TV ("batcave"), which in turn connects by HDMI to my receiver. I run Spotify and Plex Server on it, and I can control both remotely from my laptop, without needing to screen-share into retsina. Retsina is running Catalina.

The one inconvenience is directing retsina's sound output to the Apple TV, since it normally drops that and reverts to internal speakers after being idle or being pre-empted by another client wanting to airplay to the ATV. This requires screensharing.

I'm looking for a "one-click" (approx) way from my laptop to remotely switch retsina's sound output to batcave. No need to get a list of device names, it'll always be 'batcave'.

(I'm much more conversant in Unix scripting and CLI than in Applescript or Automator.)

Any solutions or ideas?