I would like to add an auxiliary input to my 2004 Chevy Cavalier factory radio. It is an AM/FM/CD (single) unit. I know that there are converter boxes out there but here is what I would like to do. Can I make a Y cable out of all of my speaker leads, tie together the +'s and -'s into two leads, and run them to a 3.5mm plug? I am assuming I will need a small amp so that the battery isn't drained on the source (an mp3 player), and will need inline switches to reduce noise when I am not using the AUX input. Can I put one inline switch on the high side of each of the four + leads? I am aware that by tying all of the +'s and -'s together, I will loose all fade and balance, but I keep everything zeroed anyway, so that is no biggie. What would you recommended for a 12V amp? What other issues might I run into? Thoughts? Thanks