Hello Chris!
I recommend disabling CC11 for expression and just using it for Velocity XFade. This way you avoid double dynamics that cause your problems of all dynamic values below mf being too soft.
Are you using the Vienna Symphonic Library House Style? In this file the values for all dynamic levels have been optimized for our sample collections. If you haven't done so yet, you can download it here:
http://www.vsl.co.at/en/68/141/460/576/655.htm
For further finetunings you can change the Dyn.R. setting of your Vienna Instruments in the Control Edit/Edit Cell menu. The higher this level is, the higher is the dynamic range of the instrument and therefore lower the volume of the low velocities. Please be aware that this level is set for every cell seperately.
I hope this was helpful.
Best regards,
Andi
Vienna Symphonic Library