The Aux input is just a basic audio input. If you connect an ipod via it's dock connector (a line level output) then you can adjust the volume on the car stereo. If you connect the ipod through the headphone jack then it's not a line level output (and hence a lower quality signal) and adjusting the volume will be a combination of the car stereo volume knob and the ipod volume adjustment. All the rest of the controls will have to be done on the ipod itself.