You can go with a mild amp to power the rear speakers and let the head unit power the fronts. I did that with an 84 Mustang GT I had in high school. It was JVC all around. In the early 90s, JVC produced an amp/EQ unit good for 50w which I mounted under the dash below the glovebox. The extra power made for a rich, full sound.

In fact I used that system in three cars altogether. I put the stock system back in the Mustang when I sold it, and moved the JVC to an 84 Monte Carlo until I was hit in it (a hit and run - someone blew a stop sign and then drove off!). I pulled it out of that car and put it in my wife's 92 Plymouth Sundance until it was totaled in yet another accident. Needless to say, I got my money's worth out of that system.

Sorry for the digression. Upon further reflection, today's head units are more powerful, so if you get an amp, you may wind up using it to power a small subwoofer, and let the head unit power the speakers in the stock locations.

My current Volvo's audio system is all stock and the head unit has a tape stuck in it. :-( I drive 100 miles round trip each day with respect to my commute, so a new system is becoming increasingly important. I am thinking of going all Blaupunkt this fall, as there is a Blaupunkt factory service center/outlet store in Bensenville, IL that has competitive pricing. I will likely wind up buying a head unit, four speakers, the smallest amp Blaupunkt makes, and a single 10" subwoofer.

Wish you well!

Kevin

92 Volvo 240 140k miles
97 Chevy Astro 124k miles