What is the best way to get the stereo to sound better without having to replace the head unit. I dont want to put a big sub in the thing, but with the speakers it has, it needs to sound better than it does. I have the Fisher Price nav system in mine, but I dont want to go ripping on the dash. Seems like every time I do that, I get unwanted rattles. Would changing the speakers and adding an amp do any good?