In Reply to: clarification posted by Josh on November 09, 2000 at 07:36:42:
BMW's changer is controlled via the "Tape/CD" button (upper right) on my head unit, and the right and left arrows (track selection). There are two plugs prewired into the passenger side of the trunk - a 6 pin and a three pin that connect the changer to the head unit and power.
I also looked into aftermarket changers...if you want to keep your OEM head unit (which I did) you are limited to BMW's or Alpine's CHM-S620 (they are the same unit). You can get the Alpine unit at a good price but the catch is you have to buy an interface cable to connect to the Z3 wiring harness...and that brings the price up to about the same as BMW's unit. I just picked up the BMW unit and installation bracket/cover for $504 (including 2 day shipping) from Pacific BMW (www.pacificbmw.com). It installed in minutes and the cover is much nicer than aftermarket options.
If you want to bag the OEM head unit you have endless options. I guess one additional option would be to go with a FM modulated device with a remote to control the changer but I wouldn't suggest this because of the loss of quality sound.