I would suggest having a few casual talks with him about how he's enjoying his life. Just because he's an obedient child and a good student, it doesn't mean that some things in his life don't bother him. He may be trying to protect you from worrying about him by remaining silent. On the other hand, he may feel just fine about all aspects of his life. A kid's healthy development is not dependent upon his playing sports or participating in after-school activities.
As for his desire to play an instrument, ask your school's counselor for some help with this issue. Playing music is not only personally rewarding, but it also provides a child with many opportunities to socialize with other musicians. You are a very involved and caring parent and you will continue to provide your boy with the love and guidance that he needs.