DNJ,
The Dynamic/Groove function on the PSR is different from the Dynamic Arranger referred to above.
Some Technics, Roland and Korg (there are probably others) have the capacity to change the style in reaction to key pressure. By pressing harder on the chord, extra parts are added, or parts are changed. The PA-80 I just sold had that function, as did one of the Technics. I can't remember if was the KN2000 or 5000.
The Dynamic/Groove function on the 9000 allows you to take an existing style, put it in Style Edit mode, select "Groove" and change the timing of the style according to the parameters you select. Thus, a 4/4 beat can become a shuffle and vice-versa. The 9000 allows extensive editing in this mode. The result can be saved as a Custom Style.
The PSR740 has a button that automatically changes the groove on the style in use. The paramaters are not easily editable as they are in the 9000, but the function is completely automatic and effectively doubles the number of available styles. (All the styles are not conducive to using this function, but a good many of them are.). One of my favorite and most used styles in the PSR8000 is one I made by simply changing the Groove of the Country Swing I, to 4/4. To makes a great Country Ballad. I also did that with the 9000, and stored the result as a user style in the unit that you now have. Don't remember what I named it, and it may have been deleted by you or Uncle Dave by now.
DonM