you do not have to change your headunit to add an amp. if i were you and you dont wanna change it you can buy a "loc" line output converter and that will tap into your rear speakers and give you your rca's then you just ahve to run a remote wire back there.
the best way to go about it though, is to purchase a new headunit with at least 1 rca output. that will give you better sound quality then the loc. its all about what you wanna do though. not everyone can afford a new HU
