Here is a simple tutorial to use letsencrypt SSL Certs with Subsonic. This is on a Debian Server
cd /etc/letsencrypt/live/<domain_name>
cat privkey.pem > subsonic.crt
cat cert.pem >> subsonic.crt
cat chain.pem >> subsonic.crt
openssl pkcs12 -in subsonic.crt -export -out subsonic.pkcs12
keytool -importkeystore -srckeystore subsonic.pkcs12 -destkeystore subsonic.keystore -srcstoretype PKCS12 -srcalias 1 -destalias subsonic
zip /usr/share/subsonic/subsonic-booter-jar-with-dependencies.jar subsonic.keystore (zip must be installed or use your compression utility of choice)
Restart subsonic
service subsonic restart
Good Luck and I hope this helps