Help Installing a JBL MS-8

I have a 2007 Prius with the nav system, which came with the JBL premium speakers.

I wanted to get more headroom along with a better soundstage on the budget of $500, so the good people over at DIYMobileAudio suggested I get the JBL MS-8, which should be capable of a higher RMS wattage, and has all the DSP stuff I need for time alignment for a nice wide soundstage.

Before I dive in and pay $500+ for it, I want to know how I should get the sound into the MS-8. Is there an adapter to take the pre-amp signal from the head-unit without cutting the wires? If not, is there an adapter to take the speaker level outputs and turn them into bare wires without cutting the connectors off? I will eventually want to sell the prius, so I want to be able to turn it back to stock without having to splice all the wires back.

Thanks in advanced!