basically the previous owner told me that the car doesn't have a cd changer due to it having a aftermarket aux cable.

So today i went and removed the hole rear panel to see, there wasn't a cd changer cable...

I'm wondering, was there actually one from standard on all S3s? and if not, how could i tell?

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this is the same as my head unit….

I do have BOSE in my car from standard. and the sub woofer is there.
I also have a odd L shaped box just below/to the side of the sub.
It has one yellow and blue hoses going into it? and 3 wiring plugs….
what is this?

Basically, i just want a cd player...