Audio Systems: Factory Car Audio, audio circuitry, amp input

Question
Hi Ernesto...Have been reading some of your answers to questions about factory Head Units, and would like your advice.  I have recently added an aux. input to my factory GM head unit AM/FM/CD unit by tapping into the audio from CD out to amp. input, inside the unit with a standard 3.5mm switched receptacle.  Works great with my XM audio output, but only when I have a CD playing in H/U to activate the audio circuitry and replace the audio output from the CD.  Can this same format be applied to a standard Chrysler RAZ head unit?  or do you know of another way to add an input directly to PC-board and using the aux/mode button on the head unit?  I will pick up a used H/U from the scrap yard to test things out before I try on my vehicle.  Any advice would be appreciated.
Thank you.

Answer
yes that is possible in almost any radio,but only if you have the time to mees with the radio or buy one from the junk yard  i
don't know you but me i need every minute of my time

if you have if yes go for it and you will learn about the radio
if not aux interface are only $65.00 and some show text from the mp3 ipod  but they cost a little more
good luck

http://www.oemautosound.com/c-148-.aspx