Comentário oficial

1) Open MIDI
2) Select MIXER
3) Click ADD
4) Click CrossFaderCurve
5) After it's added to the list, click LEARN
6) Turn the knob you want to use. It may tell you it's in use; go find that entry in the SAMPLER tab and delete it.
7) Go back to the MIXER tab and select the CrossFaderCurve again, then turn the knob.
8) Once it's saved, click LEARN again to disable it.
9) Close the MIDI panel.