Audi TT amps are line level, but there is definitly some bose trickery going on. I was able to splice in line level inputs as depicted here:

http://dougmorrison.info/modules.php?set...=view_album.php

I have since replaced my crappy sodder job with a prefab kit from here:

http://www.autotoys.com/x/catalog/AUDI_HARNESS_FOR_2002_VEHICLES_p_1194.html