Yeah, it has to do with the touch response. I have a garbage MIDI controller without aftertouch so I don't know all of the specifics.
I do know that if you turn on the Sub Osc Wheel switch it interacts with the touch response sliders on the right part of the keyboard. It may be an option to give some control for those without aftertouch on their controller. I don't know.
Turn on the SUB OSC Wheel switch, adjust the touch response sliders and then rotate the Wheel Knob. It will change the Sub OSC rate.
Other than that I haven't messed with it much.