[greglepore]

With the system off, disconnect the RCA's to the small amp then fire it back up-if some of the speakers stop playing, they are the ones being powered by it. Don't replug the RCA's with the system on.

What I would do, and the audiophiles will roll their eyes at this, is get a "bazooka tube" type unpowered woofer, and hook it up to the wires behind the seat-or get two little ones. They don't have a crossover, but naturally roll off pretty well, and are VERY efficient. And easily removable.