if you have an aftermarket headunit and you want to use subcontrol and use the subwoofer adjustments you should run a set of RCAs because the RCA subwoofer out on the deck is made to adjust only subwoofer frequencies and you can change the frequencies through the deck and turn off the subwoofer signal without altering any of the other speakers in your car. So basically if you have an aftermarket headunit run the RCAs, its more clean and easier to control with the headunit.

Right, ok I think I got it. Using the High level inputs would be for someone that did not have the option of sub control, ja? But for me, with seperate sub control, I would just run RCA wires to the h/u.

Just ordered one of those from crutchfield. Hope it help add some bass to the OEM Monsoon crappy audio.