I always thought that the HK ampf. is located inside the rear wheel arches since there were lots of diagrams showing it and written info regarding this. Guess I will go and check my car right now! (I also could not find 2 of the listed 10 speakers for HK in my car a year ago which made me crazy for sometime). Black magic indeed.
EDIT: I did check the area, nothing there just the cavity. So, either that silver module is not the ampf for HK or if it is that means that it is located differently in some cars/markets. Or, my HK sys. misses an ampf.!
Check this thread, especially post 13 from member eeghie:
http://www.1addicts.com/forums/showthread.php?t=489851
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"The mark of a great car is one whose overall competence exceeds what you should expect from its individual components and the 1M does just that", Chris Harris.
BMW 1M-SOLD-: TECH: Evolve Race+N55mids, Evolve IC, Michelin PSS, ER cp, aFe filter, CDVx, Vorshlag camber plates, BMS OCC EXTERIOR: trunk spoiler, blacklines, black grills, IND goodies INTERIOR: Alcantara steering wheel, steel pedals, custom mats, MPower e-brake.