Well, this really depends on the music you like and listen to.
For example, for Rock, you wanna go with the "U" pattern. That's high treble and bass with neutral mid tones.
Also, I don't really know the specific case of the M3 and this special audi system, but as a rule of thumb you wanna get the most sound out of the front speakers. (TOWARDS the people) with the subwoofer located anywhere you want, BUT woofers and tweeters should be pointing to the passenger.
As I said I don't know if this "custom made" system for the M3 does anything special in terms of sound delaying or processing.
Hope this helps.