I have the stock 6-disc changer/XM with the factory Bose speakers. For XM stations and some CDs it sounds good, but it seems very limited for adjusting the sound. Just a basic bass and treble adjustment. Am I missing something or is that it?

If I purchased a new head unit...like the Pioneer...or any other good one with DVD, Nav, Mp3 ... would it improve the sound as well as doing the Lux Amp upgrade or do I need to upgrade to the Lux also???
Thank you.