I'm going to suggest that they won't provide what you're looking for based on my testing of opening the masterPlaylists6.xml file on my computer and finding it was created in rekordbox 6.4.2, but I'm currently running 6.5.1 and have made changes to the playlists since that version.
You should actually be looking for master.backupX.db files instead; those would have the full database including playlists.