Here's the major things that jumped out at me first and foremost. The black levels in the BG and FG don't match. Thus, they do not look as if they were shot at the same time and place.
I took that Green plate into photoshop and looked at the channels individually. The green had the most contrast, so I threw a levels on it, and got the second pic. With a garbage matte around the outside of the cymbals, and a tight roto for the top reflective part, this would make a great matte for that area. I can't really work on it here at work, but this weekend I'll try to get it in AE at home (or maybe i'll bring in my laptop or something) and see how it works. But experiement on your own, too!
Once those two things are taken care of, it'll look 80% better, then we can start looking at other details like edges and stuff.