Audi A3 2007 Replace concert with Nexus7

[Icey]

Hi all.
I have done this to my old car.
I would like to get this in to my audi as well.

http://s13.postimg.org/cxkcjrwlj/diagram.png

Now i think i have a no BOSE system. I currently don't have an aux input or any other way to play music ( other then mp3 cd's, no cd changer ).
Now is there any way i can easily tap in to the original system whit an aux cable?
I dont want to replace my speakers, only the head unit.

I haven't taken my car apart yet so don't know what is in it and how it works .

Thanks

 

[Icey]

Sorry for the bad drawing of the setup. Basically this will make the cheap USB hubs being powered and my nexus will be charging and connected to camera, hdd/USB flash, dab radio.

 

[Icey]

Reserved