The T4 has an easy to use built-in drum mixer where it's easy to build your own kits / sound / effects. During the show both machines (T3 & T4) on stage and several comparision examples were shown. The 'hollow' or 'thin' sounding drums of T3 got much more body&details in T4.
The internet Youtube demos quality isn't sufficient to get a good impression. I was able to record some music directly from the T4 to HD ..... it sounds amazing!

I agree the Audya drums sound powerfull (perhaps TOO powerfull) but they show only a little variation per variation.

What drums a person likes is mostly a matter of taste.