If you PAN your inputs, then you are trying to control the natural panning and stereo separation of the samples coming from the keyboard. If you PAN a Rhodes Piano sample, the impending bouncing of the sound from right to left and vica-versa will become un-natural. If you listen to some drum samples, the high hat will pan left, the toms will go from left to right like an acoustic kit. You'll go crazy trying to adjust stereo panning deflection to the crowd.

I use natural panning by positioning my speakers in the most appropriate location. I point the left speaker to the right, and the right speaker to the left. I always position myself in the middle of the two.

Also, with the PMX, each channel left and right has it's own dedicated Equalizer so you could tweak the sound that way if you so wish.

For the money, the PMX is an outstanding purchase for keyboard players.