Hmmmmmm
If it were me, I'd remove that black aftermarket connector one wire at a time making sure I maintained connectivity to the white OEM connector, then I'd tackle the VW adapter between the Sony and the OEM wiring ( white connector ).

NOTE: if the Sony doesn't have 4 volt preamp outs, you will have to use the Sony speaker wires to the amp.

Of course, I could have it bass-akwards, the black connector is the OEM and the white one was added.

Did the white one go to the old radio ?