I think DS9 could go up in some classes and do just fine. I think he would love to be in a 2 grade up GT class where he could have academic discussions with the older kids. I just think he needs to spend most of his time with the kids in his current grade, at least for right now. I think he is building lots of social confidence this year. He can handle some work that is simple for him. It's a matter of balance. I think his areas of passion Math, Science, Reading would be great opportunities for him to make more challenging.
So it would appear from the above that subject acceleration may be the compromise you are talking about? If so why do you feel he can't he be subject accelerated and still pursue his sporting and extra curricular activities?