I know I am not crazy and have read in various BMW forums about aftermarket amp kits, but when I post the question here to you and Michah, I get a reply that suggests it was never available, and is in the making now.

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Author: Chris Barry
The stock 6 speaker stereo in the Aussie dellivery X5 3.0d was pretty dissappointing. After owning the car for only a few weeks I decided I had to upgrade.

I fitted BSWs stage 1 MBquarts with BSW midranges. The results were fantastic with much better definition and elimination of a really annoying cone resonance that the stock speakers had.

I did notice that the stock amp was having troubles keeping up with the MBquarts at high volumes. BSW were very helpful dicussing options and put together a amp and plug and play cable package. The MBquarts really came alive with the extra power. I also added a BSW stealth sub at the same time which really lifted the complete sound.

Installation instructions from BSW were easy to follow. Thanks for supporting the X5world community guys and keep rolling out your great products."

Would love to know more about this