The factory stereo isn't the greatest anyhow.. and the speakers are less to be desired. Best thing to do is to rip out the entire unit and get a proper system in. Why bother trying to bandaid up the existing unit - spend some cash and get a bumpin' system.
I like the ones you can get in the Japanese X-Trail.. very slick.. or this Pioneer..
http://www.avic-n1.com/