Hook up aftermarket 6x9's to factory amp?

I installed my clarion 6x9's the other day, but unfortunately, they only have 1 set of wiring hook ups, where as the factory 6x9s had two sets of wires running to it, one from the factory headunit and uses crappy 20-guage wire, and another set of wires from the factory amp that's in the left rear of the trunk.

Problem is my clarion's don't have a second set of wiring prongs to hook up the amp to, so I'm left with them being powered by just the headunit and the poopty 20-guage wire, I'm broke so does anybody know how to hook up the factory amp to these speakers? They sound clearer and are a bit louder than the factory 6x9s I had in there before, but they don't hit as hard because they are grossly underpowered right now.