OK I have halion Symphony Orchestra VST pack.
I notice you can get expression maps for the instruments.
http://www.steinberg.net/en/support/content_and_accessories/expression_maps_for_vst_expression.html
In the same page there are expression maps for other software manufacturers VST sounds.
I don’t have VSL, but would the VSL expression maps work on HSO or am I completely barking up the wrong tree!