Looking at the two big electrolytics in the picture Derek posted HERE I have to wonder if the factory 540i amp is really a 4 channel or two channels with some more over-engineering to emulate 4? Also, does any source show what impedence the factory crossover presents? I bought a 4x50 for the fronts and a 2x200 for the sub, but since the sub is a DVC with a max power rating of 300W, it may work better to use the 4x50 bridged for the sub and the 2x200 for the fronts (if the amp really turns out to be only 2 channels). All at 4 ohms, but both amps are old 90's PPIs and both will work fine at 2 ohms (except driving a parallel-wired DVC sub bridged). As a side note, I noted that someone posted that a 15" tall sub box was the biggest the E34 would accomodate. I wish I had seen this before I mounted mine in a 16" tall enclosure two days ago. Guess I had better warm up the saw.