Don't know about MD changer with Wave, but referring to your original question I specced Boost cassette + CD Changer in my Cooper, and in addition to the points raised above about extra power & speed related volume option, the boost cassette player has powered eject/ff/rw, dolby and with the MFSW (which I also got) you can fast forward/rewind to the next track from the controls on the wheel, which I don't think you can do with the wave?
I'm sure someone will correct me on that last point if you can control the cassette from the MFSW with Wave.
It's a bit steep at 135 quid for Boost, but I got it anyway!
