minor update -- tried one bav midrange in the back doors and it made no difference vs. stock. in fact, stock sounded a little better. so i'm keeping the rears stock. funny, i've read that at least one of the pro installers that do a lot of bmws (systems costing thousands) will not touch the back door speakers as they don't really make any difference up front according to him.

only thing left for me is to see if there is any way of getting better base out of the central woofers without adding an amp. even though everyone says it won't work, i'm going to try an sws-8 off of the stock headunit. will post results.