another option is running an external eq that has subwoofer control. i have mine ran that way bc not only do the HU eq's usually suck balls, this gives me a lot more adjustability over my sound. audiophile problems. anyways, i have a dedicated subwoofer VOLUME control on my eq, and also the bass knob that controls the GAIN. two different beasts, just wanted to clarify that. i never adjust the bass knob, in fact i'll disconnect it eventually when i build my final system, but once my gains are set, i just adjust the volume for clean power throughout the volume range.