A:Answer If you still have factory speakers, they're not necessarily going to let the aftermarket stereo operate at full potential because OEMs tend to have higher impedance ratings. It would be best to replace the speakers with aftermarket, 4Ω-nominal speakers IF you still have 16-year-old factory speakers.
If you did install aftermarket speakers, check the polarity. If they are wired in reverse, the sound will be playing out of phase. Just one speaker out of phase with another can make things sound really weird.
I haven't installed a car stereo in over 20 years so I have no idea what kind of quality to expect from these newer things, but I used to swear by Pioneer head units and Infinity components. As long as you're taking the time to do it right, I expect you should be able to improve the sound quality without too much hassle.
