Beth - Sorry, got distracted by the math crisis. DH is supposed to be taking DS for his flu & meningitis vaccines, but instead he is screaming at DS about the math tests.

DH would do well to SHUT UP and let me handle it.
So, Miles, instrument.
I played cello in middle school and LOVED it. I had no interest in band. I wanted DS to play a string but he refused. Percussion.

And he loves it. Visions of marching band dance in his head and all that sort of thing. If he LOVES orchestra let him stay in that. If not, see if he wants to try something else.
Let Miles choose. If the rental fee for another instrument is prohibitive then have a heart to heart with him and find out what he wants to do.
The only thing I have been successful at pushing with DS is Theater classes. He balks, but he really does LIKE those classes, so when he balks I ignore him. With other stuff, when he says NO, he means NO, and if I push he is a complete snark every step of the way.