@Basbleu : The degree of support from need-based aid should become apparent from the NPCs.
Does Amherst offer much in the way of Japanese language/culture courses? As a benchmark, some of the other schools suggested in this thread offer 15+ courses in the field, enough to exceed what your son would ever be likely to take.
Regarding social factors, your son would be entitled to make his college his own. Whichever school he attends, it would be his as much as anyone else’s.
Look at Macalester too. Excellent music and Japanese programs were on my son’s “gotta have” list and Mac made the cut.
I’d like to suggest a lesser known, somewhat selective option the University of Mount Union. Very well-known for the Division III football program, it also has an excellent Japanese program as well as an excellent music program. Located in Alliance which is about 1.5 hours from Oberlin and 1.5 hrs from Ohio Wesleyan.
Bard should most definitely stay at the top of his list - it is one of the top composition programs in the country - and is completely accessible to the non conservatory students - including studying with the same composers. It also has a fantastic Asian Studies department. Most families I know have been very satisfied with their need based aid, even happily surprised when Bard offered more than other schools. It’s the merit aid which is more problematic, as it varies depending on need.
Of the other schools mentioned here, if he’s serious about studying music composition and thinks of it as a possible career path and for graduate school - I would second only Lawrence, Williams, Wesleyan and Univ. of Puget Sound. Possibly Carleton (I do know a composer who did her undergrad there.) I don’t know what it would be like to study composition at Oberlin not in the conservatory - however, for a double degree that would be a good choice. Swarthmore and Tufts are other schools to look at for composition. If he chose a double degree path you could add quite a few universities, such as Michigan.
Feel free to PM me about the composition department at Bard (my son was a double degree student there, Composition and Classics.)
Just wanted to let you know that my somewhat nerdy, liberal D feels at home at Lawrence and has lots of friends who tend toward the nerdy side. I wouldn’t describe it as sporty/ traditional. When my D was looking we heard it described as more moderate than Oberlin, but I don’t see it as traditional if by that you mean preppy or more conservative. There are a lot of students from the Midwest there and I think that gives it a laid back down to earth quality. Check out the Great Midwest trivia contest that they hold at Lawrence every winter for a fun campus wide nerdy event. The conservatory and music there are a real draw. Despite it being a conservatory it is very open and fluid to the campus as a whole and lots of non music majors are involved in the conservatory there. I’m happy to answer any questions you might have about Lawrence if I can.
Willamette received a lot of hits on this thread, but by count of Japanese studies courses, the school only approaches the top compared to other colleges mentioned (Where fairly readily available, other posters should feel free to correct, or add schools):
Colorado College: 19
Hamilton: 19
Willamette: 17
Amherst: 14
Oberlin: 8
Beloit: 4
Not sure what the basis is for the best music school recommendations in post 24. Hamilton, for example, graduated a future Pulitzer Prize winner in Music Composition, and seems to have an open program (and great facilities) that would be excellent for the study of music.
Re #26, Colorado College appears to offer several .25 credit “maintenance” courses. Their course total, by standard measurement, seems to be ~16.5:
Updated
Hamilton: 19
Willamette: 17
Colorado College: 16.5
Amherst: 14
Oberlin: 8
Beloit: 4
@merc81 - I’m very knowledgeable about music composition programs. It isn’t a question of whether it’s a nice music department for performance, or whether courses are open to non BM students, or those majoring in music, as much as it is who exactly is teaching there and what the range and breadth of courses are.
Colorado College might be a good option, as well, although I really only know about their New Music Ensemble and not the composition department itself. As for Hamilton - Melinda Wagner graduated in 1979. That’s awhile ago now. 
In looking at their music offerings, it’s pretty standard basic stuff - which could be perfectly fine for the OP - it really all depends on how serious he is about composition. If he’s satisfied with that level of offerings - then he should probably focus more on the Japanese offerings first, and the composition courses second.
The list I gave is for serious composition students planning either on a career or further advanced study at a high level. I did not mention the Ivies for this OP, but they are almost all worth exploring, as well, for music composition. As well as some of the larger universities without Schools of Music like the University of California, Berkeley or San Diego.
It is not impossible to get into the top graduate programs coming from a less well known undergraduate composition program - but it will depend on the talent of the student, as well as the advantage they take of summer programs, networking, performance opportunities, etc.
Seconding Bard, Willamette, and Earlham.
For music and Japanese, look at St Olaf. (Merit possible).
Japanese language and Culture Courses (adding Earlham, St. Olaf and Bard)
Earlham: ~30 (not bad . . .)
Hamilton: 19
St. Olaf: 18
Willamette: 17
Colorado College: 16.5
Amherst: 14
Oberlin: 8
Bard: 7
Beloit: 4
@SpiritManager : You appear to be very knowledgeable regarding music programs. It would be silly of me to question your informed perspective. However, I’d say Melinda Wagner’s Pulitzer is not irrelevant, regardless of when it was awarded. Schools with “better” music programs than Hamilton’s may NEVER have graduated an equivalent winner. So premises must be examined from time to time about what ultimately may be achievable by graduates of various colleges.
@Basbleu, I hope you and your son have a chance to visit Williams and/or Wesleyan. The rich kid, country club stereotype is no longer a reality at northeastern colleges. Although there are certainly students from wealthy families at all selective colleges (everywhere, not just in the northeast), the vast majority are academically accomplished middle class kids from all over the country, most of whom receive some level of financial aid.
Both Williams and Wesleyan have excellent music and excellent Asian studies departments (including Japanese). Double majoring is encouraged. For example, here are Williams’ course offerings in Japanese.
http://japanese.williams.edu/courses/
The campus cultures and environments of these two schools are quite different, though each might appeal to your son for different reasons: Williams because of the rugged individual, outdoorsy culture; Wesleyan because of the quirky, activist culture.
I agree with Hamilton,Wesleyan and Bard. All three are quirky in different ways and have excellent music opportunities Also check out Vasaar excellent music and it is easier to double major there since like at Hamilton- few distribution requirements.
@merc: I get how you counted the Hamilton courses because they are nicely listed in the East Asian Languages and Literature page. Not sure how you only got 8 classes at Oberlin. If the OP in interested in language only then I count it as follows:
Hamilton has a nice program. It offers three years of language and fourth year of selected readings/translation–8 semesters.
Oberlin offers 10 semesters of Japanese language including two advanced level courses and not counting any thesis prep class, so if you come in with any Japanese at all, Oberlin would be a better place than Hamilton.
Oberlin also has the Shansi Foundation which offers fellowships in Asia. http://shansi.org/
Oberlin and Earlham are both part of the Great Lakes College Association. Earlham is the Japan specialist and Oberlin is the China specialist (though no slouch in Japan). All GLCA members can participate in each others various programs abroad.
I’d encourage the OP to visit Oberlin and see for herself the culture. It’s a pretty exciting place if you are interested in music and East Asia.
@qialah : In Oberlin’s case, the site initially indicates four Japanese language courses. An additional step is needed to see the rest of the offerings. I simply missed this. (My tallies were preliminary. I had invited corrections in post 26.)
My son and yours share a lot of interests (music, Japanese culture/anime, outdoorsy-ness, nerdy/non-preppy) and he’s headed to U. of Puget Sound in the fall. I think it should be high on your list.
One of their flagship departments is their School of Music. There are a lot of music majors, and the department is fully accessible to the full college community (i.e., not a separate conservatory and don’t need to pursue a B.M. to take advantage of all opportunities). Not sure about composition specifically, since my son is interested in performance, but I’d be surprised if their offerings are not well above average for a LAC.
Moreover, they’ve got some pretty unique opportunities for a kid especially interested in Japanese. They’ve got a special 9 month Pacific Rim trip that happens every 3 years, and they’ve just started another scholarship program for kids specifically interested in studying in Japan for 9 months. Check these out at http://www.pugetsound.edu/academics/departments-and-programs/undergraduate/asian-studies/
Also, the outdoors culture at UPS is HUGE. Mt. Rainier is a dominant presence on the horizon and multiple backpacking trips are organized every weekend. They even have a special outdoor-themed freshman dorm. This was a big draw for my son.
Finally, they offer quite generous merit aid, but for folks with a lot of financial need, they may be less generous than some other LACs. You should run their NPC to see if it can work for you. Good luck!
Keep Oberlin on your list. They give merit money, and their Japanese department is strong. You can also take music classes and lessons even if you don’t go the Conservatory route.
As far as the wonky politics go, my middle of the road son is doing fine there. Most kids are not at all like the spoiled, demanding ones who make the news.
“I have looked at Amherst Et al but somehow I think he’d feel like a fish out of water on the east coast surrounded by the country club set”
That’s interesting, because Amherst and Vassar are the two most diverse elite small colleges in the country, in both economic diversity and racial diversity. More so than several others in discussion here.
^ That would be news to the usual ratings giant.
Well, they both were awarded a big national prize due to combining elite status and socio-economic diversity.
(None of the colleges ranked on the first page are anywhere near “elite”).