can this be done ? UPDATE
 

thanks for ur replay
this is what iam think.

So if i could get the cd changer to decode the mp3 info
off the cd's and feed the id3 tag info back up to the head unit, would it
come up on the display ??

(1) The IP BUS has left\right audio in\outs, so i would be able to put the
decoded mp3 audio back to the head unit.

(2) Also does anyone know that when u select "ext" changer do it bypass the
int mp3 decoder in the head
unit ??.
I have tested (1) and i can put audio in!!
Not to sure about (2) but i think it will bypass the int mp3 decoder.
So now it begs the question are there any hardware mp3
decoder chips that can give id3 tag info, that are simple to use, low
component count and make a single side pcb.

The next thing is how to get the head unit to talk to the
modded cd\mp3, i need some big help with the IP BUS
system.

Can anyone help with any diagrams for cd\mp3 cd changer and just plain cd
changer, to see how things
are done ???

Thanks all for reading this
Howard