Hi guys,
This is my first post, be easy on me!

I recently traded in my 330ci for a 4.6is X5 (2002). I hate the stock nav unit in the X5. I have the MKIII version with a 6 CD changer. The nav is slow and the cd changer doesnt play MP3's. I could upgrade them both, but its fairly pricey. Now, I have a Pioneer Avic Z2 with a 30gb HD that I pulled from my 330. I would like to install it and replace all the stock components in the X5. I called a friend of mine who owns a car audio shop in Boston, he says the only way you can do that is if you replace all the speakers and amps in the car because they are connected through an optical cable? Is this true? It doesnt seem like its for real but I just wanted to toss back ideas with you all and see if I could get any input from people here. If anyone has had success instaling an aftermarket Nav unit replacing a stock nav unit. Thanks in advance!

Brandon