LOL...Yeah, blaupunkt has been doing the audio for VW for a while now. If it is a 10 speaker system chances are the system is probably using a factory amplifier that is driving all 10 speakers individually. I've never seen Blaupunkt or any other similar player have the capability to run 10 speakers (one being a sub) from the head unit itself unless they are using low powered component sets (2 speakers running through a passive crossover) per channel or running a speaker with a really weird ohm load. Most players will only run at 4 ohms stereo (4 channels total) with the exception of Bose Premium Systems, Mach systems etc. I couldn't say exactly where to look in there for a factory amplifier (because Passats aren't all the common here but I can find out), but you could probably test the speaker leads from the head unit to see what ohm load you are reading at the deck which will give you an idea if an external amplifier is being used. If you get no reading, then chances are an external amp is somewhere in there. If you do get a reading like say 4 ohms, then you can use something like a AA battery to do a quick "pop test" to see if the wiring runs from the head unit directly to speakers. A little pop with confirm that which means no amplifier is in line. From there (if the impedance is 4 ohms), you can just replace whichever speakers you want for something with a little quality or you can replace the player with something with a little more tunning capability than the Baupunkt. That is something you could probably change yourself being a mechanic. Other than that, you would be getting into aftermarket amplifiers, higher end speakers that can take more wattage and a really good subwoofer to give you nausea
Let me know if you think of anything else...