I have a question:
How about contemporary composers?
I would like uploading some pieces from a man who still is alive. Is this OK with GEMA ?
How do you do in this case?

We already have pieces by several living composers and this has been no problem so far (we don't post their scores). My guess is no living composer in their right mind would object to having their music recorded.

Not sure if we have anything to do with GEMA. I'd never heard of that until now and we have never had them commenting on our site. But perhaps you should check if the composer in question is a member of it ?