nascar,
Wishful thinking!?
I doubt very seriously that BMW would have been so generous as to provide preamp outputs on a production vehicle? I agree that it would be very nice, however, not very probable?
You can however, install a new amp and sub(s) using the stock sub speaker outputs (using converters to get line level outputs). I've done this on my BEAST and the improvement was tremendous!!!
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Andy
2000 Imola M5 / Black Nappa - Titanium Trim