SA and VST articulation voices are not just samples but programs as well.
Megavoices are Midi loops with additional effects added by touch and additional notes.
Not ideal for sampling, therefore I would suspect that the Gigasamples are just the basic sounds of these voices.
BTW Are these samples the ones originally made for the Mediastation?
Live entertainment, Real Ale, Great Scenery, Great Beaches, why would anyone want to live anywhere else (I�m definitely staying put).