I have had the same struggles and managed to get JGitSshClient working. Here is an minimal example that puts everything together: https://github.com/david0/mina-ssh-over-socks/blob/main/src/main/java/Main.java#L22
I would prefer if MINA would come with SOCKS support build-in, since recent JGIt >=6.0 needs Java 11 minimum.