MarTT

This took several weeks of research here on the forum (thanks Steve Schwing and spoiledTT - KrusTTy) and finding parts (some trial and error) but the end result is complete and amazing! I loved the look of the stock HU but after attaching an XM radio and other aux devices I wanted an all-in-one solution. The Alpine CDA-9820XM is currently the only XM-integrated HU on the market (there is one for Sirius as well, not sure what brand).
Anyway, the <a href="http://public.fotki.com/martt/audi_tt/mods/radio/">completed how-to is in my fotki</a>; here is a quick overview:

Metra 70-1787 wiring harness soldered and taped to Alpine harness -
<img src="http://images12.fotki.com/v243/photos/4/41970/2928815/radioinstall027-vi.jpg">

Out with the old -
<img src="http://images12.fotki.com/v252/photos/4/41970/2928815/radioinstall056-vi.jpg">

All plugged in for a test - it works!
<img src="http://images14.fotki.com/v247/photos/4/41970/2928815/radioinstall064-vi.jpg">

Completed install -
<img src="http://images12.fotki.com/v252/photos/4/41970/2928815/radioinstall090-vi.jpg">

I have the aux mini plug tucked away next to the tunnel to plug in my iPod Nano (the HU does not control the iPod, it simply outputs whatever is plugged in to the mini plug. So now I have all in one unit, XM, CD, FM/AM, Aux and the sound is excellent. I'll need to adjust the faceplate for a little better fit but overall I'm very happy with the upgrade. <a href="http://public.fotki.com/martt/audi_tt/mods/radio/" target="_blank">See my Fotki for the complete how-to.</a>