I have Chris Hein Horns and they sound great! Probably the best of it's class, IMHO.
The areas I would like to see developed (in Kontakt scripting) is more velocity control in real-time. For example, I would like to be able to use cc information to play soft hits very fast, without triggering the loud hits, for a really dynamic performance.
As far as I know I have to change the velocity level before or after I track the parts so there is a lot of tweaking. It would be sweet if I could use the volume pedal to control velocity as I'm playing.
What controller are you working on at the moment? There shouldn't be any reason, with a good MIDI keyboard, why playing quickly means you have to trigger the loud samples.
On the other hand, if you're getting nowhere with a keyboard, then many instruments are now set up for breath and wind controllers, in which case they work exactly as you are asking for (if I've understood correctly); i.e. the keys only convey pitch information, and dynamics are determined by a continuous controller, such as cc2 or 11. Even without having a wind or breath controller it should be possible to use the instrument's breath controller mode, and use your MOD wheel, or a pedal, to send the cc that would normally be sent by the breath controller.