In my experience, some of the most talented kids leave high school music band, orchestra and ensembles in favor of higher level performance (and often classes) outside of high school. That depends of course on your location. Are you in or near a city, a university, or a conservatory prep program?
Has he taken any piano? A piano teacher who teaches theory along with piano can be helpful. Conservatory prep classes in theory ( or a local college) can be helpful. Does his high school offer theory? AP music theory won’t mean he can skip theory once in school, but can be one way to learn what’s needed. Theory tests at auditions are for placement purposes, generally, so no need for him to stress.
Has he had any exposure to “new music”, meaning late 20th and 21st century composers? Jazz? is his small ensemble work classical? Does he envision himself in a band, or what are his goals?
You might want to read the essay “Double Degree Dilemma” that is posted above. The author covers many of the options for studying music. Music major in a BM or BA program (BM is approximately 3/4 music, BA is 1/4), music minor, double major, and double degree (BA/BM or BA/MM, 5 years). He can also major in something else entirely and continue with lessons and performance (and still be eligible for grad school).
He can major in music and still have access to all the jobs available to those with bachelor’s degrees, and access to grad school and professional schools like med, law, business or nursing school.
If he has other academic interests, he can still pursue music while majoring in that area. If music is what he loves and wants to study, he can do that in the music-focused environment of a music school or conservatory, or in the broader curriculum at a college or university. The general music major usually includes theory, music history, composition, ethnomusicology, musicology, technology and so on. Every school is different: some BA programs include performance in one way or another. Search websites carefully.
State universities tend to have BM programs available, and if he likes to play in band, those are a great option. A school like U. of Michigan is top notch for music.
Schools like Bard, Oberlin, Lawrence, Ithaca, Tufts/NEC, Harvard/NEC, Berklee/NEC, Rochester/Eastman, Johns Hopkins/Peabody, BU and many others offer the best of both worlds with double degrees.
In later high school, some talented, kids deemphasized academics as priorities but still get into selective schools because admissions appreciates dedication to music and the contributions musicians can make to the mix on campus. For others, it makes sense to keep all options open, as long as the stress is not counterproductive. If your son is overwhelmed he might want to lessen the rigor of a few classes, and/or withdraw from high school music activities, depending on where his own authentic interests lie.
Summer programs can be really helpful in clarifying some of this. BUTI is one program. We always suggest Walden School in Dublin NH, which is focused on composition but has classes during the day on various topics, including new music. Yellow Barn, Bowdoin, Brevard are some others (I haven’t checked these for percussion). You could check and see if the Berklee summer program would suit him.
I just checked and Oberlin has this http://new.oberlin.edu/office/summer-programs/index/percussion/ which could be really amazing for him and open new vistas.