Can anyone check whether the extra brightness in the T5 is primarily due to some changes in the default Mastering Presets (EQ and compressor), or programming something inside the style?

I guess the best way to check would be to have the T5 play a T4 style (copy it over), and see if you can hear any difference.

Several people have mentioned the extra top end as a minus, perhaps it might be something as simple as backing off on any extra high end boost in the EQ or gain on the high band of the multi-band comp?

Personally, a little more crispness to the Tyros sound is OK in my book... makes things sound a bit more live, a bit less CD-like.