Backing up music from 2 laptops dilemma

Up until now I have been using an rsync script to backup my iTunes library to my server.  This has been a great solution for backing up my single laptop, but the tides have changed and Kat is starting to add a lot more music these days to her iTunes.  That being said I really want to end up having a central location to backup all of our music while weeding out the dupes.
With out much thought my first idea was to setup the same rsync script on her laptop as I used on mine …. but that totally wont work as each time we sync it will remove the other persons files.  My second idea was to complicate things really bad but installing a sync script on both of our laptops and then nightly have the server ruin another script to parse out the dupes, in the end that solution wont end up being logical since every sync will re-upload the files that were removed for being dupes.
If anyone has a working solution to backup two Mac laptops iTunes libraries to a linux box with out having duplicate data or causing a ton of bandwidth issues with every sync I would love to hear your thoughts.
For reference I have included the current, possibly bad rsync script that I have been using. This can probably be simplified and expanded on to not sync movies, tv shows, and iphone apps.