There are two ways to tell if the box is hacked in this case:
1. Apply the hack using the DMS tools, put the DMS in the box, let it run - if you don't hear the announcement and your music starts playing, bring the DMS back to the cradle and have a look for a logs directory. In their should be a file specifying if the hack has ever been run.
2. Put your own disk in the DMS cartridge - use the DMS tools to load up the appropriate firmware and see if it works!