You might want to post on the music major and math/computer science major forums.
On the music major forum, make sure to read the Double Degree Dilemma essay under the Read Me thread posted near the top. It covers different ways to study music, including double major and dual degree.
For double degree, consider Oberlin, Bard, Lawrence. Oberlin also has a relatively new Musical Studies program for non-BM students that offers access to conservatory resources. These three (and a few others) are very supportive of double degrees (in fact Bard requires conservatory students to do one) and the music campus is not on a separate campus (Eastman and Peabody are not as well integrated with the college).
I would add Harvard to your list along with Tufts, for double degree in Boston. Harvard’s is a BA/MM. Or apply to Harvard without the double degree. MIT might interest you as well.
If you are talented enough to apply to NEC and Eastman, then you are good enough to submit a music supplement for colleges where you would get a BS/BA, including Harvard. A recording/video, music resume, and letters of recommendation related to music. Music can sometimes really enhance your chances.