there an adapter on ebay for dirt cheap that will allow you to go from the AFM rectangular opening to the circular one needed for the cone filter then buy aluminum sheets, make a prototype with cardboard so you know where to cut and fold and do it.
in my opinion its a fun project. who cares if it gives you hp increases or not. at least it cleans up the engine bay and makes this nice true to bmw sound.
then post pictures when you're done!