I fitted one in the S4 and it really was plug & play, everything worked first time.
A bit dated now compared to the likes of MP3 players and ipods but essentially does the same thing. I like it
Paid about £160 for a new one from US ebay a couple of years ago.
They're not made anymore and there's no support for Vista for the software which you use to set up all the albums on the removeable hard drive, so make sure you have access to a PC with XP on if you're thinking about getting one.
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Present: S4 B8 avant, fully loaded, MRC Stage2, Milltek non-res, KW springs
Past: S8 D2 FL, S2 ABY coupe, RS6 C5 saloon, RS4 B7 saloon, S4 B5 saloon, S4 B6 avant, all gone but not forgotten