yeah you gotta keep in mind a head unit amplifier is small so don't expect miracles out of it.

if you installed http://www.sonicelectronix.com/item_76451_Kenwood-KAC-6406.html for example you would get more out of the speakers.

you'd also need a 4 channel amplifier kit and a roll of speaker wire. its quite a bit of work if you rewire it completely, but its worth it just to get rid of 16 year old wiring that wasn't meant to handle much power to begin with.