Soul Music is the one where specific instruments are mentioned. Buddy (Imp y Celyn) plays a sort of hand held harp before he finds his guitar in the phantom music shoppe. Glod, the dwarf plays a type of horn, which I seem to remember is refered to as a Crumm Horn and the troll bangs various sized rocks together. Pianos are mentioned as are banjos (Nanny Ogg). And of course, various places inculding the university and the opera house have bellows-driven organs.
"Goodness is about what you do. Not what you pray to."