For that subtle volume control and sharpness, I use a function on my midi sequencer, I can change the velocity of the sound... unless I sampled it. I don't know if there's anyway you can do this. Usually I wind up with a thicker sound if I double up on them, I only do that in certain cases when I'm looking for that particular sound, I don't think it'll make the kick sound sharper, but muddier.
Maybe I'm wrong, anybody else?