I had the same set up and it was the worst sounding stereo in a car I've heard in a long time. I had a stereo shop replace the head unit, add a 4 channel amp, replace the dash speakers with some Alpine units and add some Infinity 6 inch component door speakers (and their cross overs). The inside of the doors were also covered in dynamat for better sound and no vibrations.
I love the way it sounds now. Here's what the component speakers look like installed.