Oscar,

BSW put together a package with a Alpine V series amp and a plug and play cable. The cable went between the head unit and main wiring socket using plugs and sockets compatible with the BMW units. The amp had high pass filter adjustments and gain on the front/rear channels. The stock 6 speaker head unit signal improves markedly when its not driving any load.

Write up and pictures here.

http://www.xoutpost.com/bavarian-soun...tml#post228110

Chris.