Armbruster has composed music, often with Charlie Brissette, for the animated series Ren and Stimpy, Sitting Ducks, and The Adventures of Jimmy Neutron. He has written or arranged songs for multiple Disney albums, usually for the Mickey Mouse characters. He appeared on-camera as an improv pianist in Man in the Moon (with Jim Carrey as Andy Kaufman), for which he wrote the song "Route 69." He performs regularly at Colombo's Italian Steakhouse in Los Angeles.