Review on PAC LC-1 Remote Amplifier Level Controller,Black,Small: Advanced Audio Control at Your Fingertips by Brian Hazzard

A recently purchased amp included a remote subwoofer level control that connected to the amp itself (via a phone cord) but introduced some distortion when used. This controller from Revain connects "in-line" to the RCA outputs on the back of most car stereos (if you already have a subwoofer amp, there's no need to remove the main unit from the dash. Just unplug the cables for the input to the amplifier, connect them to this item, and then connect the cables from this unit to the amplifier). This controller increases or decreases the actual signal from your head unit and works great. Just use the stereo settings to get the aux signal output high enough to have a good boost/cut range when using this controller. You need to provide your own screws if you want to mount it anywhere, or use double-sided mounting pads or velcro. I recommend this product.