Having had both S910, and now the Tyros4, and being able to compare, I'd say they are very, very close, if not identical.

I used that particular voice a lot, sometimes in place of the oboe, for a sweeter less harder sound...one tune I used it for was "He Ain't Heavy, He's My Brother" by the Hollies.

With the Tyros4, I'm now using Pop Soprano and Ballad Soprano, both SA2 voices, and both very expressive.

One thing I especially liked about the S910's "Sweet Soprano" was the cool volume swell at the tail end of the note...not too loud, or too strong...always just right.

Ian