Hiya,
I'm new to Audi and just picked up a 2012 S4 last week. I'm selling my 2008 BMW M5. The S4 is a great car so far, but one thing I couldn't believe is that it didn't have Bluetooth streaming. Seriously, I purchased the car just assuming it had Bluetooth streaming only to find out when I got home that it didn't. I was going to add a Tune2Air, but remembered that my new phone supports Apt-X, a new Bluetooth standard that's higher quality than A2DP. The sound quality is noticeably better (to me) than the Tune2Air. The only drawback is that you can't control the music from the steering wheel. Here's what I did.

The Parts:

http://www.amazon.com/Littelfuse-FHA...ELQ/ref=sr_1_1
Add-a-circuit so we can power the Apt-x module


http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1
USB Power for the adapter


http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1
The MMI Aux adapter


http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1
The Apt-x adapter


http://www.amazon.com/Install-Bay-Te...gauge+3%2F8%22
16 gauge 3/8" terminal ring connecter for the ground


http://www.amazon.com/gp/product/B00...?ie=UTF8&psc=1
3.5mm to 3.5mm female to female adapter to hook up the MMI adapter to the Apt-x adapter


http://www.amazon.com/Install-Bay-BV...utt+connectors
16 gauge butt connectors to hook everything up


http://www.amazon.com/Coleman-Cable-...=16+gauge+wire
Extra wire to give us some room to work

Here's the process:
1) Open the passenger door and take off the panel on the passenger side dashboard to expose the fusebox.
2) Remove the rearward purple fuse holder and use the bottom fuse to install the add-a-circuit
3) Feed the wires for the USB power box through the small square hole in the glovebox that connects to the fuse box.
4) Ground to the bolt on the firewall at the top of the fusebox using the terminal ring connector
5) Mount the USB power box in the glove box
6) Plug in the MMI adapter to the car, then the female-female adapter, then the Apt-x adapter
7) Pair the Apt-x adapter, and listen to high quality streaming music!

You don't have to worry about charging the adapter because it's hard-wired, and everything stays in a neat little bundle in your glovebox.

Thanks,
Ryan