Awesome, thanks. Using the wiring color scheme from the X5 tips page makes completes the picture for me to identify the wires to connect to each speaker.

In case others are not familiar with the German colors scheme:
BR brown
GE yellow
GN green
OR orange
VI violet
GR grey
SW black
WS white
RT red
BL blue
TR transparent
In the diagram the module N9 is the radio (or the Business CD unit), H55 is the left front midrange speaker, and H54 is the right right front midrange speaker, both being on top of the dash.
Signals TLH+/- are for the rear left woofer
Signals MTHL+/- are for the midrange speaker/tweeter, rear left
Signals TLV+/- are for the front left woofer
Signals HLV+/- are for the front left tweeter
Signals HRV+/- are for the front right tweeter
Signals TRV+/- are for the front right woofer
Signals MTHR+/- are for the midrange speaker/tweeter, rear right Signals TRH+/- are for the rear right woofer