You are correct, the setting on the alpine unit is called "subwoofer volume" I believe. At 2v the subs are doing nothing basically. Without cranking that up you barely hear them. I swapped between the rear pre outs and the sub outs on the deck with the fader set full rear to see what the difference was, nothing too noticeable and with the amps built in cross over using the sub pre outs and playing with the setting gave me a bit more control vs hooking up to rear outs.