Sounds to me as if a large state school with a good school of music is his best option, because of the wide variety of available academic majors. Again, if continuing to study his instrument is that important to him, the first factor is the teacher at the school. My kid, who originally had been intent upon conservatory, then school of music with access to great academics, and then finally chose to attend a tippytop school with a vibrant performing arts scene, but no music performance instruction at all, started the process by considering all the teachers in the country who taught at decent academic institutions. Kid then eliminated locations they wouldn’t go to, and teachers that they (by sound or reputation or lack of availability) didn’t want to study with. This narrowed the list considerably.
Some good U’s with good schools of music and good academics are reputed to be places where one can double major in music and academics pretty easily. When my kid was looking (not your kid’s instrument), they found that McGill, BU, U Md, and UConn all fit this description for them, in addition to having an excellent teacher for kid’s instrument. Yale is an option if they can get in, because of the presence of the Yale school of music, which is only masters level, but students can take lessons and play in ensembles. At the time my kid was applying, they were in transition for my kid’s instrument’s instructor, so kid didn’t apply, but otherwise it would definitely have been on the list.