I have just bought a leather interior for my S1 C5 2.0 HDI 90 BHP .I checked under the seats for the cables and they are present and also the fuses are fitted for them in fusebox B. On inspecting the wires I also came across the wires for the CD changer and I traced them back to the head unit and they were connected.I will be taking delivery next week of the interior and will let you know how the fitting goes
Jay