Have the stock CD/radio in the '05 QC. Been noticing that some of the sounds/instruments on cd/songs aren't coming thru. Would this be a speaker or CD problem?

 

You're best bet is to replace both the head unit and the speakers. Factory head units have a very poor signal to noise ratio, so the amount of music you get is limited. To make matters worse, your factory speakers have paper cone woofers and are very easy to blow. Replace the factory speakers with a good set of aftermarket speakers and see how you feel about your music then. If you're still wanting more, look into replacing the factory radio with a unit that has a fairly high signal to noise ratio and a good signal output (16-18 watts rms per channel). That will give you a good basic audio system. After that, you're looking at adding amplifiers which will allow for a great sounding system, but you're also looking at a higher price tag.