First of all, pardon the "intrusion" into your S4 forum, but I posted here a few weeks ago looking for info/help on getting my iPod into my allroad.
I was first intrigued by jyoteen's post about getting the iPod installed, but was a bit disappointed to see the use of an RF modulator. I was able to find a cable that allows you to input a clean source via RCA input jacks in place of the CD changer. Not sure if your S4s have this, but I'd bet it's an option for you guys too.
Anyhow, check out the XPOST if you're interested.
PS. I wanted to get a S4 avant, but family requirements made me get the allroad... in two years the allroad goes to the wife and I plan on getting the new S4, whatever shape it takes.