Most Palace of the Dead music comes from other places in the game and then randomly plays within certain floor sets of the palace. A few floors have fixed music unique to Palace (floors 1-3, 47-49, and 97-99 for example).

51-60 are all tracks from elsewhere. As far as piano/rock music goes I'm guessing it's the Dueling theme (from Duels at Wolve's Den pier) or A Bloody Reunion which plays in some of the Warring Triad storyline scenes.