Either they went the "cheap way" or they were being very cautious in fully implementing audio based styles.

Korg has completely shied away from using this technology, as has Roland, although the latter appears to be less involved with arrangers lately, so perhaps Yamaha is just putting their toe in the water before taking the plunge.

Even Ketron hasn't got it perfected yet, being that they need to use midi based sounds to reproduce certain complex chords, although, I must admit, they have done a pretty good job disguising that fact.

As I said before, I'm quite content with my Tyros4's entirely midi based styles, especially since the editing (most important to me) and storage is without issues, and the use of mega voices (and SA/SA2 voices) still gives an extremely realistic representation.

Ian