Caltech should be on his list if he has the grades and test scores. Small and suburban. As I recall from the tour, the student guide mentioned that 60% of the student body played a musical instrument. He also joked that if you were a theater major, they need you.
No merit at Caltech, though, so that puts it in the same category as Harvey Mudd – awesome, but pricey.
Thank you all so much for the suggestions! My son really likes Harvey Mudd, and I think he would thrive there. We only need to figure out a way to afford it if he gets in…!