On Linux, add --https-port=4443 (or any other port) to SUBSONIC_ARGS in /etc/default/subsonic (Ubuntu/Debian) or /etc/sysconfig/subsonic (Fedora/RPM).
I initially used the 4443 port, and also the 4040 port (what Subsonic is currently using), but I get a 404 error error for each:
https://www.dropbox.com/s/qymrl9hr8ph4m ... r.jpg?dl=0
If it helps, my current firewall settings for the router, concerning the pi:
https://www.dropbox.com/s/x3qlv72skc977 ... 1.jpg?dl=0