I was recently looking for a good spot to install an aftermarket Sirius radio on a TT, but couldn't find much so I got creative and ended up with a really nice final install so I thought I would share if anyone else is looking to do the same. I ended up installing the radio faceplate using a custom metal bracket (I found on ebay for like 10 bucks) in the center console below the ashtray, only a small amount of hacksaw'ing reqd on the bracket to get it to fit right but it came out looking really nice. I can post some pictures if anyones looking to do the same. The face of the radio is out of the way and not blocking anything, accessable, and you can run all the wiring right down the center into the console and behind the dash so you don't see any of it (did a hardwire to the fuse box for power, as well as wiring it through the CD changer with a 3 way switch so i can still use the changer on the 2001 BOSE stereo and have two other aux options, one for Sirius and one for the iPod).

I used the "SoundGate SDSISO Volkswagen & Audio Dual Plug & Play Aux Input 1998 - 2008" harness kit. I have the 2001 BOSE radio w/ the cd changer behind the driver's seat. It was a little difficult to find the kit online for cheap, best site I found was  http://www.hifisoundconnection.com/ which has it listed for $45.50. Really not too difficult of an install, even though it looks like a whole lot of wires when you get the kit.

Hope this helps.