For natural sounding reverb, nothing beats convolution, which makes use of impulse responses (IR). These are recordings made in real acoustic environments which can be used to make a virtual instrument sound like it’s in an actual physical space. Kontakt 2 ships with a large collection of impulses, and you can probably find lots more by searching the web. But too much of a good thing can end up sounding awful!
If you are running multiple instances of Kontakt 2 instruments, the best way to keep things sounding natural is to use the same impulse on all the instruments. That way the final mix will sound more like real instruments playing together in the same acoustic space.