I went from a 5.9 Grand Cherokee with headers, exhaust, throttle body, and intake mod's to the 4.8 X5. What impressed me with the X was the power curve - punch it from standing still and it just keeps pulling hard thru the shifts all the way ! I like the fact the shift points are at redline. It is definitely faster than my Jeep, although much quieter.
I agree with your comments on sound system - pretty mundane for a vehicle in this class.