I'm using a stock headunit with USB input. I just piggybacked a line out converter across all 4 channels, leaving the original wiring in. It sounds okay but you will lose bass above 40-60(max). Note you have six speakers: Rear parcel shelf, front doors and in your dash just under the windscreen. I believe they are 2" speakers with a in-line capacitor to run high frequency. They run in parallel off the front speakers. Mine are stock. For the front 6x9's you're gonna need some MDF to mount on. I used 1/4" MDF mounted to the door frame, followed by a 3/4" MDF oval to give me a total of 1" clearance from the window. I have 3 3/16" (3.2") top mount depth speakers in. No issues with clearance/door trim. The rear speakers will hit the plastic cover so use something like 1/4inch MDF to make the baffle plates, and just watch out for the boot springs. No issues with parcel shelf cover/boot clearance. Here's what my front door looks like ;) http://instagram.com/p/b_BJhhAJ6o/#