I would say this is a Kontakt matter. I use Battery and I can assign several samples to a
cell and set different velocities for each sound in the cell, but the velocity to volume
is set using a separate modulation parameter. I would guess that you can remove the
velocity to volume parameter somewhere in Kontakt, but I've no experience of the programme
to be able to help you.
--------------------
http://soundcloud.com/richie-royale
http://www.mixcrate.com/richieroyale