Aux Input - Blaupunkt RCM 127 Casablanca

I've successfully identified the audio line input channels on this head unit and hooked them up to a mp3 player.  However, when I select aux on the head unit and play mp3, I get no audio to the front speakers additionally the head units audio controls have no effect on the output.  Selecting the source to radio cassette brings all 4 speakers back on line mixing the output with the mp3 player!?

I know the aux input I'm using is from the cd changer connector and that of course I have no changer connected, but I would have thought this would not have affected the output in this manner.

Any advice gratefully received.

I soldered a fly lead (LH audio, RH audio and audio ground) direct to the aux pins on the headunit terminated with a 3.5mm stereo jack to the mp3/cd player.

I've looked further for a pinout diagram of the aux/cd changer connector for the Casablanca to no avail.  I have all the original documentation that came with the unit but it doesn't show a clear enough diagram of the pin assignments.