I did my Aux input hack today to great success. I seem to of done it slightly differently to most. I took of one of the blank buttons on the dash and mounted a switch and a 3.5mm socket in it then connect one of the sides of the switch to the socket. The out then went to an male xlr with left right and a common ground the other side of the switch went to another female xlr with all the 3 ground binded at the switch ( The idea of the xlrs is on the head unit side there would be a male out from the cd player and a female input to the amp so you could plug them together and the head unit would be the same as when you started =).
In the inside of the head unit i just removed the bottom panel and where the cd left and right channels came into the amp i cut the tracks wired left and right to the amp which would go to the out of the switch and with the other cable to a couple of solder pads further upstream of the cut trancks and the ground to a hand ground pad that was right next to them.... =)
So in conclusion i now have a switch on my dash that switches between the in dash cd and the mini jack input on my dash......
the only oddites being that when I came to look at others ideas my head unit seems to be of a different design to everyone elses on the inside but the same on the outside.
********* The only catch is when the cd comes to the end there is 3 seconds of silence as it goes back to the being (oh well beggars can't be choosers)*********
http://homepage.mac.com/jrumball/PhotoAlbum1.html (forgot to take some of the amp side soldering opps wil do at some point soon though =) )