Every T2 style I have works seamlessly. I haven't even opened a style where one voice is missing.
The S910 will also play T3 styles, but many have voices missing with substitutions. The keyboard makes these substitutions rather intelligently, often finding another Mega!Voice.
This is a nifty program to revoice a style
http://www.jososoft.dk/yamaha/software/revsty/. The Tyros 2, on the other hand, will not play a style that has been saved on a PSR-S910. You'll have to use a format converter (
http://www.jososoft.dk/yamaha/software/sf2c/index.htm).
Beakybird