Here is a link to help make the stock stereo system sound better. You just have to access a "hidden" mode on the head-unit and change 2 settings. If you read through it one of the posters has data graphs and what not on the sound quality from the different modes.
http://forums.nasioc.com/forums/showthread.php?t=2317060
http://forums.nasioc.com/forums/showthread.php?t=2317060