Debug mode:
Select "Classics", then move Up or Down to any slot. Hold LS or RS while pressing Right or Left to bring up a 12 digit alpha-numeric display. This "code" represents the piece of music in that slot.

Here is a partial list of what they do, listed from left to right:

0 0-4 Determines name of piece (Imperial, Aspen, etc.)
0 0-F " "
0 0-F Determines "style" of play (smooth, syncopated, etc.)?
0 0-F " " ?
0 0-F " " ?
0 0-F " " ?
A A-X Melody seed
A A-X Key (A#, C, etc.)
A A-X Music Type (Fugue, Adagio, etc.)
A A-X ?
A A-L Instrument (Piano - Trumpet)
A A-G ?