Hey, I bet they simply wired it exactly like the original unit, which means the sound is coming from only the left and right front speaker setting on you HU. The best situation is to cut those input wires at the amp as described in several posts. It is confusing at first, but if you study it carefully, you will fiquire it out. Mine is set up with front chanel going to amp input for the doors and the subs are set up for the sub out to the other chanel on the amp that goes to the rear subs. I used pre outs for all my connects and turned off the HU internal amp. Major sound difference for my car.