The SuperNatural technology is VariPhrase based, I'm pretty certain of it, because I can clearly hear the "sample", especially when you press the same key over and over, you can hear the "staticness"... VariPhrase can also be compared to wavetables in that the technology stores extra data about every single-cycle of the sample... that's what the VariPhrase encoding does in it's Solo encoding algorithm... you can hear it when you slow the speed down of playback... I bet that SuperNatural is nothing more than specially prepared and encoded samples, that has extra articulate synthesis for the way pitch, time and formants are handled relying on your playing technique... I believe this because the last V-Synth, the GT actually had SuperNatural in it's infancy... it was just called AP Synthesis instead of SuperNatural.
Also if you look at the features of the INTEGRA-7 it hints at it... it's sample based, because otherwise they would not have included all those SRX boards in it, allowing it to play back standard PCM as well... the Supernatural synthesis is so close, that the engine probably lends itself to PCM based playback easily as well.