The biggest problem with them is that the mid-range speakers in the front doors are prone to self-destruction at relatively low volume levels. The largest contributing factor is the automatic volume adjustment as the car gains speed (Tony: Wow! that’s a cool feature, isn’t it?). I blew my own that way! Adjust the volume level in the driveway, make it onto the freeway, and KA-POP!
BTW, if you have that annoying feature, I just learned how to fix it while I was researching the Harmon Kardon (HK) stereo. First, you start with the stereo off. Turn it on, and hold the "m" button for approx. 10 sec. The serial # of the radio should appear on the screen. Once it does, use the + and - buttons until you see GAL 1-6 . Then use the < and > buttons to adjust it up or down. 1 is the lowest change, and 6 vice versa. I believe that should also work on British BMW’s as well, even though it was explained for an American M3.
These are some photos of the Harmon Kardon audio system:
