Yes, I'm familiar with Music Together. I was a parent to the kid who was at the edge of the group and was saying after how he didn't like the way Jacob waved his scarf or the way Hannah moved the pillows, etc. Group classes with preschoolers weren't his thing. And, that's okay because as you get older that really only comes up as a parent or if you decide to be a preschool teacher. What would be the adult equivalent of Music Together? Cocktail party? Dancing? Plenty of people hate both of those.

What is obvious to me in retrospect is that what he wanted from a class and what I wanted were two different things. He wanted content. He was much happier attending lectures and concerts for adults. I wanted him to socialize. Thing is that it really was not a social occasion and he was overwhelmed with that experience. I learned later that group classes are actually not that helpful in making friends. http://www.amazon.com/Good-Friends-Are-Hard-Find/dp/096220367X

I'm not saying you should quit. I think there can be a lot of value in experiences like Music Together and it sounds like he has things to work on. What I would suggest is to not get ahead of yourself thinking this is a problem that means he needs a diagnosis. There are MANY kids who find this sort of class doesn't work that well for them as a preschooler. If you think he has sensory problems certainly getting OT is not a bad idea.

What I would suggest is more important... Help him have plenty of predictable routine and gentle opportunities to expand what he can tolerate. Work on helping him be more flexible and optimistic in his thinking bit by bit. Acknowledge his upset but don't dwell on it or revisit it. Before the situation talk through what to expect emphasizing that things may change. Try out giving him an assignment of something to look for. Could be something neutral - report back how many people were wearing red, or something positive, tell me the song you liked best. He can give you an assignment too. Whatever, just something to focus on and it will help guide your conversations in a more positive direction.

Oh and get this... guess what happened to my kid who was the at the edge of the room as the stressed nonparticipant in Music Together? He's in high school. His hobbies: music and dance.