I have no idea what the definition of the difference between normal and natural sound is. Yamaha imply natural means extra long samples, or maybe more samples per voice. This does not strike me as a description of the 9000 normal voices, compared to cool sweet etc. I am just telling you the facts that Yamaha claim natural voice for the high end Clavinovas, but nowhere do they claim natural voice for 9000 or tyros.

I saw the tyros preview in Frankfurt, the official new products launch and the first official tyros launch in the UK and have talked with various Yamaha people including one of the designers of the tyros about the voices. The thrust of the launch was mega voices, no mention of natural voices.

Since the 9000 has 32 MB of wave rom it is extremely unlikely that it could accomodate the natural voice samples of the high end Clavinovas in addition to sweet, cool etc. As I understand it the majority of the increased wave rom in tyros compared to 9000pro is dedicated to the mega voices which take a lot of space. The other voices may also benefit from some increased wave rom, but if this is to the level of their definition of natural voices, why not publicise the fact? They have not.