Hello guys, I just grabbed a sweet s-line B7 cabriolet down here in south Florida for my wife. This (sort of) replaced her '13 A5 we had to sell when we had our son last year and got a suburban. To get to the problem.. she wanted Bluetooth and a better stereo interface for the car, so I bought an aftermarket and what I thought was the right metra wiring harness. Turns out the symphony stereo has a completely different setup in back than I've ever seen (pictures to follow). I've scoured the internet to find a diagram of how to hook it up, but to no avail. Anyone know where I can get some help? If not, stay tuned for a write-up on how to.
Thanks guys

 

Pictures attached

 

I had the same problem with my stereo! I have bose and it is just as annoying. if you want to get a complete plug and play system, this is where you want to go. the only place I found that has a wiring harness that actually works!
Enfig Car Stereo - iPod XM and Sirius Satellite Radio & Auxiliary AUX Audio input specialists | Page 1 of 1
I purchased a metra harness and had the same problem. it flat out did NOT work. but these guys have everything. they even have an antenna adapter that works as well, as it actually uses both antennas. their steering wheel adapter works as well. I purchased a HILO harness, which was expensive but it has alot in it. these stereos require basically a mini computer to make them work with aftermarket head units, which is why the harness that works is so expensive. Not to mention that their customer service is very good. they spent an hour on the phone with me (after business hours) trying to work out the installation with me. so if you have any questions, they will do just about anything they can to help!

I would not recommend trying to wire it yourself, as the most you can get without getting special noise insulated power feeds and some complex wiring is the front speakers. which works but is not what you want. fell for it on my old A4 and just wired the front speakers and I kind of regretted it. When I got my newer B7 A4 with bose I just went for the plug and play from enfig and haven't regretted it yet other than the initial cost being more than what I wanted to spend. You can try to wire the rear speakers. I eventually found a full stereo wiring diagram (like the whole system A to Z) which was difficult to read and when I finally found the rear speaker amplifier turn on wire it made a hell of a noise when I tried to turn it on. (hence you need to find a noise insulated power source or make one) which requires alot of extra time and work. But overall I have wired many stereos in many cars for friends and none has been as complex as the audi ones.