PSR3K. Just found two interesting settings.
FUNCTION / STYLE SETTING / SPLIT POINT.

1.The first column STOP ACMP. Set this to STYLE and the 3K with ACMP Button On (but no Style Playing) you can change the bass voice used in the left hand by select CHANNEL ON/OFF. Press upper of the 2 Bass tabs to change the Bass voice.
NOTE. (I think) Fingering needs to be set to A1 FINGERED for this to work.

2. The forth column STYLE TOUCH set this to ON and the 3K Style volume will respond to how hard you play.