i had a kenwood that gave me the option to turn the internal amp off.. i had to turn the headunit off, with the ignition still engaged mind u.. basically so u can still see the clock.. then held "menu" or "audio" for a few seconds.. can't recall exactly.. but it was the same drop down menu as selecting the speaker sizes... and scrolled down until it had the option "internal amp on/off"...
i know u can turn the sub off by holding down on the right control knob/stick thing