Yeah, I made a huge mistake with my bondo. I should have taken it slower and read more. Hindsight is 20/20, and for those following my install, learn from my mistakes please! I will clean up the inner edge, but it will not be perfect. If it does not look salvagable after all my cleanup efforts, I will start over. The double din kit is pricey, but I can get it for around $50 online I think (paid $80 locally).
As for connecting the audio, I found this and think it may work... http://www.cardomain.com/item/PERSVEN4?vq_id=none
It looks like it will take RCA input and send it to the factory wiring to the speakers. I am still trying to figure out if my amp is in the HU or seperate. Paul H is a Audi tech and he is going to check my VIN and give me the wiring diagrams and such. Hopefully this will shed some light on the audio situation.
As ssmiley1 said, the adapters are made for an aftermarket HU, which would be powered. Since I will be using my USB soundcard outputs, it may not be enough power. Maybe a small amp between the USB soundcard and the interface adapter, that way the RCA output to the adapter would be powered.
Still searching, and thanks for all the reads and replies...