Offizieller Kommentar
For starters, I wouldn't recommend using two different computers unless you're doing a full backup from the "master" and then restore to the other as the "slave" with no intention of taking the changes made on the slave back to the master. It just gets sloppy.
What you can do is export music to the USB drive from the master, then take the USB to the slave computer, right click on the playlist from the export USB device and then "import" that playlist and all the music. Then you at least have a copy. You can repeat that as often as you need, but again - not ideal.