You should check out some of the software from propellerhead. It is kind of expensive I think but they have some really good drum synth's if I remember right. It has been a while since I looked at it all actually. The one I used to use was called Rebirth, but I think they had a product called HammerHead too.
Some of that stuff is not available on Linux, but I have some synth and drum apps. I decided to play my own drums on this. I prefer real instruments where possible.