Dave, On the Yamaha PSR3000 and Tyros you can play a midifile and while it is playing you can select any style or variation available and push the start button for the style section and the drum track used for the song file will be substituted for the current style and variation selected and the tempo will be sync'd to the song tempo. You can select any of the four variations and fill ins and they will change in real time while the song plays. At anytime you can hit the stop button and the original drum track will play and vice versa.
George Kaye
Kaye's Music Scene
Reseda, California