Where did the samples come from? No two instruments are actually identical - in fact they are completely different. Also, no two people will play an instrument in the same way. If you're combining samples you are just summing together audio, but in the real situation you describe there is a much more complex thing happening - the interaction between the sounds and the environment. The sound from one drum will even resonate the body and skin of another.
I can't say I've got the answer, I'm afraid. I think these problems are some of the key issues surrounding sequencing orchestral type music on computers, and why when creating sample libraries we still record sections as well as individual instruments. The idea of physically modelling instruments and objects is the closest thing we have to a solution, but I don't think we can yet model the complexity of the physical world to this degree.
Here's a few ideas off the top of my head though:
- Record individual samples from ten different drums
- Take IR's from ten positions in a room
- Use subtle resonant filters add a bit of colour to the drums
- Connect it all up with a (very low energy) feedback network, like with waveguide synthesis - this can model some of the energy transfer between different parts of the room
- Add in some distortion or overdrive to simulate the interactions between the sound waves.
Probably easier to record some drummers! But it would be an interesting experiment to try anyway.