Since you are getting the RIGHT1 (midi channel 1) sound on your KN5000 when playing the PX7, I can only assume that your midi connections are correct, so . . . my guess regarding your question is that the "touch sensitivity" on your PX7 Piano is set "higher" (must press keys harder to produce louder sound) then on your KN5000. Try changing the PX7's keyboard "touch sensitivity" so you don't have to press the keys so hard to produce sound.
Hope this helps,
San Francisco Bay Area, CA