Really hammer they keys when you are playing it. Lol. I have trouble getting anything below the full velocity.
You can change the velocity settings in most synths similar to the way you would map cutoff to a mod wheel for example. This is usually in the modulation properties and velocity is usually defaulted to volume in the amp section.
I don't know whether the sonar midi plugin still comes bundled with x2, I am not at home at the mo to check, but I remember velocity mapping with that in 8.5 to a certain degree of success.