This amp is a 4 channels amp. What exactly do you want to do? just adding an amp to power a subwoofer? If that is what you want to do you can indeed use one of the two pairs of channel to drive 2 subs (2x 75W) or 1 sub (1x150W). You can plug your amp following the instructions provided in the article on the main page. You do not need LOC (Line Output Convertor) with the JL 300/4. There is a 'high/low' switch on the JL amp for each channel pair. Select "high" for the channel you want to use to power the sub. If you plan to power one single subwoofer you will have to bridge the channel pair you wantto use for the sub. By bridging you combine the output power of 2 channels to drive one single speaker. Hope that helps