I made an unpleasant discovery after purchasing a Bose Mazda CD radio off of Ebay. The non-Bose has internal amplifiers and the Bose does not. It works with an external amp and low impedance speakers. Upgrading isn't as simple as switching out the head units even though the plugs are the same. I decided to take them apart to see if the CD mechanisms were the same (my old radio wouldn't eject the CD's). They weren't, but I figured out what was wrong with my old radio while I had it apart. I now have an extra Bose radio with CD player, but at least the radio in the cars works OK now.