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.
Anyone know what "European IP" means? They announced a while ago that they working on new titles for Virtua Fighter, Golden Axe, Crazy Taxi, and a few others, so I'm assuming those are the "Legacy IPs." What is their European IP? The Total War franchise? The developer, Creative Assembly is from the UK. That just seems like a weird way to phrase it, if that's what they're talking about.