If you really wanted to do it this way, I think for any reasonable speed, you'd want the actual tagging to happen on the empeg side, without the FTPing to and fro. Which would mean "some program" running on the empeg would open a socket and listen for requests coming from, say, the SYLT plugin, and tag the files accordingly.

The thing I just don't like about this approach is that it only edits the file on the empeg, not the local copies that we all keep for when our empeg disks die. So you do all this work to write something to add lyrics to your MP3s, then they're gone the next time you need to re-sync. I don't know how to work around this problem, because to my knowledge neither emplode nor jEmplode has a concept of keeping a local directory structure in sync with the player (so it could update both the local and empeg copies of the file.)