I have allready removed the stock HU in my 06. The stock unit really doesn't put out any real usable power. If you wanted to keep your stock HU and add aftermarket speakers with an amp you would have to get a line converter to tap off of one of the speakers. Since the stock HU does not have any RCA'S for an amp, the line converter uses the signal from a plain old speaker wire and converts it into an RCA signal for an amp. If you choose not to amp the aftermarket speakers and keep the stock HU they probobally wouldn't really sound any better than stock. I am running the factory speakers with an alpine deck right now (no Amp) and the stereo sounds a lot better than it did with the stock HU. I can't wait until it gets a little warmer out so I can install my amps and subs.