Disklavier

Has anyone found a way to allow for placing individual CD tracks into storage?  It's great that we can access/play the many .mid/.fil files stored internally or on external USB drives, but it would be so handy to cherry-pick the best tunes off the many pianosoft CDs and make a master play list of this music.  I understand that Mark IV systems can store audio CD tracks (up to the internal drive limit), but how about 
E3 and 850 owners?  

Can the controllers even play .wav/mp3/?? file formats? Or is it hard-wired to just read off the CD player unit?

Happy Holidays!