I would be concerned about this, too, unless he has other diagnosed disabilities that would contribute to the meltdowns.
First-- could he be hungry? Low blood sugar? Can you bring a good snack and tell him to eat before he says anything to you about the night?
I would also give him some stress relief techniques-- tell him he can take deep breaths, he can visualize all the happy things that happened that day, he can visualize a happy, calm place, he can make a gratitude list-- all in efforts to prevent the meltdowns.
But honestly, I would not put up with that behavior one more night. I realize you like the social experiences he has. But controlling his emotions is probably more important at his age.
I would tell him if he does it again, he's done with band. Period. He's not allowed to rile up the entire family with that kind of behavior. What has the normal consequence of that been throughout his life? I think you might be surprised that he has more control over his behavior than you think-- if he realizes there's a strong consequence.
I also think you might want to consider a counselor who can help him with his emotions, and to help your family help him.
