I'm pretty sure that the only thing that qualifies as a dupe is the same exact file (FID) as stored on the Empeg's hard disk.

For instance: If you upload a song once, then copy it to three different playlists, those three copies are dupes of the original song. They're just links to the original FID of the first copy you uploaded. Those copies will be removed from the playlist when you shuffle-play the whole unit, so the song will only appear once in the shuffle.

But if you accidentally upload the same song again (for example, if you re-encode it and you forget to delete all four instances of the original before uploading the new copy), then the Empeg doesn't know it's the same song and you'll now have two similar-sounding copies. As far as I know, it doesn't try to pattern-match or use tags to determine whether or not to dupe-remove it. They're two different songs as far as the Empeg is concerned.

___________
Tony Fabris