Okay, a few questions. First of all, my current car is a '97 BMW 740iL. Won't be doing any work on this car since I'll be trading it in on a '97 or '98 BMW 540i soon enough, but since the two cars use similiar speaker setups I've been investigating exactly what's possible. In doing this, I've noticed a few things. The system is powered by a stock amp in the trunk, not by an amp in the headunit. Apparently this is true on the 540i as well. Next, the head unit isn't a standard size and can't be replaced since the OBC controls are in it. What is a standard size is the unit with the equalizer controls. It would seem that if I wanted to put a new head unit in I'd have to pull this out. Of course, this would leave me with not only useless radio controls still present in the cabin, but useless steering wheel controls as well. Besides becoming somewhat attached to having controls on the steering wheel, having the radio controls be present but non-functional would drive me crazy. I'm just a sucker for things looking stock (on the bright side, if I were to replace the equalizer with a head unit there's a piece of wood trim that slides down and blocks it anyway). My solution to this is to work around the head unit, but I'm not sure how well this would work. What I want to do is replace the stock amp in the trunk with two new amps. One will power the front speakers the other will power a subwoofer. The rear speakers will be removed all-together since I really don't have any need for rear fill. Moreover, I'll be replacing the front speakers with a new set of components and adding a single (probably 10 or 12") subwoofer in the trunk. Finally, I've learned that there's a 10-disc MP3/CD changer that can be swapped with the standard 6-disc CD unit on the 540. It'll work with the stock head unit, although tracks have to be searched through one by one. It's a bit of a compromise, but I think I'll manage. Okay, so that's my plan. With any luck, this means I'll be able to keep all of the stock functionality, but gain a significant upgrade in sound quality. The main hurdles that I foresee are getting my hands on a wiring diagram for the stock amp in the trunk (although I've already located the outs from the stock head unit, not sure if these will be in the same place on the 5, though) and taking the risk of having the stock head unit seriously degrade the overall sound quality. Beyond this, does anyone who has worked on BMW sound systems in the past foresee any problems? Or anyone familiar with car audio in general? Since I'll be trading the vehicle in sometime in the next month I'm hoping to have enough planned ahead that I can start purchasing things immediatly. BMW really did a poor job with their stock sound systems, so I'm hoping to not have to deal with it again on my second one.