One thought I had was to try to login to the local IP address on the port I've dedicated to Subsonic, but I had trouble getting AVSub to login to that address. It's the same address the Subsonic server redirects you to, though. The syntax is very specific, it has to be exactly http://184.108.40.2069:1234/
. Don't forget the final slash, and don't put anything after it.
However, even over the local network, it's glacially slow. My desktop computer doesn't have that problem - it's able to download a whole FLAC file in about a second.