Most of the time the volumes depend on what equipment a file was created or is played.

e.g. XG (yammie standard) recorded songs can be played on a GM-machine, but the sounds/volumes 'behave' different.

On my Tyros came some (custom-adjusted) styles that were changed by someone. They have another EQ- and volume setting :
Much louder bass volume and Low-EQ turned UP.

Probably done by someone who's speaker system produces not enough LOW audio.
On my system however it sounds TERRIBLE.....

I skipped all those 'Adjusted' styles.
The original PRO-styles sound amazing with bright, clear and deep sound.