I am an Ipod guy (I own 4 of them) so I am not familiar with the Zune. I run a micrsoft-free household. The iPod has a fixed level audio out on the 30 pin connector, I don't know if the Zune has a connector, I never looked at one.
I am thinking that this will work:
http://www.compusa.com/products/product_info.asp?product_code=342620&pfp=external&tabtype=rv#review to get audio out of that thing. Then what you do, assuming you don't have the in dash 6 or a changer, is get one of these:
http://www.abtelectronics.com/product/18137.html to get audio into the CD Changer port behing the radio. I use this piece along with a JL Audio CL-SES to route audio from my iPod, SAT Radio and my Rosen 10" flip down.
FM modulators are asstastic and should be avoided at all costs!
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2006 CRD
http://www.UtahPowderCoatings.com/ http://www.gorecon.com/ I'm kind of a big deal.
RL rear bumper, ARB front bumper, Mile Marker winch, Power Tank, Skids by Mopar & Skid Row, RL Super Skink Sliders, 235/85R16 MTR, Air Flow Snorkel, DTT, 4.10 gears, Frankenlift II, Katskin leather, JL Audio stereo, Rosen video.