Its not only the voices, but espescially the effects that are of very much improved quallity and take all excisting sounds and styles one step higher...
On top of that the number of SA voices has been doubled... The new organ voices are of stellar quallity and there are a bunch of new e- pianos.... And then there is the new ensemble voices, which from my point of view is the best new part of the T5, yet this is highly arguable..
On top of that the 50 new aodio styles are really good ...
I think soundwise it is the greatest update to a yamaha totl arranger since the release of the PSR8000