I use Funkwhale, which I have liked, but my use case is just streaming music through my laptop and listening with headphones. I don't think there is a client available that will run on your Autonomic streamer.

Funkwhale does have a subsonic API, so you could use a subsonic client, but you mentioned that didn't quite work before. (Is that what you mean by __sonic? I haven't actually heard that term.)

Funkwhale is nice, but I think for most people it doesn't (yet) offer any useful features beyond what Navidrome has, and probably even lacks a few things that Navidrome has. Funkwhale's main appeal is that you can follow someone's music library via the fediverse, although there hasn't really been a lot of use for that so far. Version 2 is coming soon, though, and adds a whole bunch of new fediverse features.