This is the original subwoofer assembly from my 97 540 with the DSP (premium) sound system. It is two pieces. First is a Nokia plastic box with a metal lid that holds two dual-coil 5 inch subwoofers that are 8ohm. The second piece is the cover that makes it look like a part of the trunk. Piece one fits inside piece two, and then both mount under the rear deck and transmit sound through holes cut in the deck. The sealed Nokia box has never been opened. This unit worked fine in my car, but I opted to replace it with larger subwoofers.
I am thinking $150 and buyer pays actual shipping.