The music is played with the:

Pee Java: The flute responsible for the distinct sound of the phleng muay
Ching: Cymbals that help with the tempo
Glaawng: The drum

Live bands are the best. Some play a more "jazzy" style where you can actually distinguish a tune. It's much better than the cookie cutter CD that is played at 95 percent of amateur shows (and many in Thailand).