Hi Walt,
I had exactly the same problem that you are having when I moved to the KN6000. The pedal which originally was used on the KN3000 didn’t work on the 6K. A new pedal solved the problem. There is one other thing that I find some players forget to do. That is, press the expression pedal all the way forward and adjust the volume with the slider when playing a sequence or a MIDI file. This will prevent the volume from taking a jump during playback.
Happy tunes,
Frank