I would like to know what people mean by when they say "tap into the rear speakers". In the picture attached, the left diagram is hooking up sub(amp) and the rear speakers from the same wire. The right diagram is taking the wires going to the rear speakers and routing it instead to the amp. Which diagram is right? Or are they both wrong? I just want to add a subwoofer to the stock headunit while making sure the all the stock speakers still work. Thanks in advance.