Glad to help. The Common Application actually has a music supplement your son could use, if he's interested (my sister is also applying to colleges this upcoming year, and this is what she's using). The link to this is
https://www.commonapp.org/CommonApp/...Supplement.pdf. There's also some information on the Vassar College website about how to submit music supplements (
Vassar College || Guidelines For Optional Art Submissions) and a form for students interested in submitting music supplements to fill out which is virtually the same as the common application music supplement form (
http://admissions.vassar.edu/pdf/fre...n.pdf?refresh).
And no, I personally doubt that a "sub-professional" tape would hurt his chances of admittance. If the music supplement seems like it might be a bit over his head, however, the YourSpace segment on the Vassar Common Application Supplement might make more sense. It would still allow him to show off his talent, but wouldn't be as formal an undertaking and wouldn't be listened to by a member of the Vassar music faculty.