Thanks people.
Feenix, isn't using CC11 simply increasing the volume of the sample so that if, on a single p sustained sample, you increase CC11 aren't you just increasing the volume of the p patch. It's difficult to explain but if you have a two second note starting p cresc to mf which then moves to another 2 second not starting mf decresc to p. If you use CC11 you simply increase the volume of the P patch and then move to an mf patch and decrease the volume of that patch. There qill be an audible difference between the timbre of each patch. Ideally I want to use a dynamic patch where the cresc/decresc is recorded into the patch but, inevitably even with VSL, there's only so many of those they can record and they don't fit all situations by a long shot.
Also isn't expression and volume the same thing whatever CC theyre assigned to.
Anyway i shall experiment with expression.