Hi Scott,
Well, my friend, I can only say, that except for the main piano sound, the Tyros2 and S900 sounded very much the same to me, when played through my sound system.

The drawbar organs SEEM to be same, at least to my ears, although the organs for both the T2 and S900 don't sound much like a real Hammond to me.

The SA sounds appear to be identical (minus the aftertouch)and, in my opinion, are the most useful ones from the Tyros2...they are excellent.

Hammond's XK1 and XK3c, which I tried last week, are the closest to the true Hammond sound...they smoke the other clonewheels by Korg, and Roland, but carrying another instrument(or module for that matter), is a hassle...if I was going to carry anything else, it would be an 88 note hammer action digital piano...but I haven't found one under 30 lbs that I like.

I am more than pleased with the sound, reliability and overall performance of the S900.

Ian