Sony CD changer and VW Gamma radio

I asked sci.electronics.repair about this but didn't get very far.

I have a 98 Passat Estate with Gamma radio (Gamma on cassette flap) and Sony
CDX-T69 CD changer fitted in the boot. Problem is that although the CD
changer has power (magazine loads and ejects OK), the radio reports "No CD
chnager" when the CD button is pressed - except for this the radio appears
fine. I understand that there will be an adapter somewhere (AVGS003MK2). At
the radio end this is a blue connector that fills half the upper socket (of
three) - the CD end has a round connector and two phono-type connectors. All
look OK. I don't know whether the CD ever worked as the first thing I did
after buying the car was to replace the battery. So,

1. I had to recode the radio - is there anything else I need to do to get
the radio to recognise the CD changer?

2. Where is the adapter likely to be? I can't see it behind the radio or in
the boot.

3. Is the adapter just a means of changing conenctor type or is it an
electronic device which might have failed?

4. Are the phono connectors at the CD end just the audio signals? If so,
given the CD has power is it reasonable to assume it is faulty as this
connector would also supply any signals the radio uses to detect it?

Hope someone can help!

KotF