First, select ''Classics'' then move up or down to any slot, then hold RS or LS while pressing right or left. This will bring up a 12 digits alpha numeric display. This code represents the piece of music in that slot.
Here's a list of what they do(listed from left to right):
0 0-4 Determines name of piece 0 0-F '' '' 0 0-F Determines style of play 0 0-F '' '' ? 0 0-F '' '' ? 0 0-F '' '' ? A A-X Melody seed A A-X Key A A-X Music type A A-X ? A A-L Instrument A A-G ?