I was quite disappointed in the stock sound system in my A4, I bought my wife a 2002 BMW 325i and found that her system was ten fold better than mine, this was something I could not have.  I decided to go to Traffic Jams in LA and dropped about $2,500 on speakers and amp.  I kept the stock head unit because I still wanted to make it look stock, but my friends the  Diamond Audio speakers are the way to go.  The component speaks are all kevlar cones and they are by far the best speakers I have ever heard in an automobile.  Without a doubt if you are looking for a new sound system and clean sound go with Diamond, the five year warrenty doesn't hurt either. What else can I say you just have to expirence them for yourself...