The little rotary button does the fader duties for front/rear. If you plan to in the future to place the factory stereo, I would advise you to splice into the wires coming out of the rotary button. Now, if you plan to go all out (specially with a high end unit like that, I'm a Pioneer fan
) in the future, then wire straight from the unit so you can better use the crossfading and all that the head unit comes with. If you need any help or questions just PM me.