Hi Steve,
thanks for your interest in MIR SE!
Like always, the Presets have to be seen as starting points for your own creations, depending on your needs. As long as your system is powerful enough, you can add as many samples to an instrument as you like.
The only limit to keep in mind is the maximum number of 32 instruments within MIR SE (opposed to 128 in Vienna MIR).
HTH,
/Dietz - Vienna Symphonic Library