Yup :) I've had a Gamma IV in my Scirocco Mk2 for about 6-7 years for exactly those reasons - green backlight, subdued styling. And I got fed up with having my radios nicked.
There's a changer control on the back, as noted. No other aux or preamp apart from whatever you may find on the pinout for the CD. I've never checked so YMMV.
Gamma IV was made by Philips (and perhaps others according to some websites... hmmm) - but when you say or search for Gamma you'll mostly find the Gamma V which I think was a Blaupunkt unit, commonly found with blue backlighting (Mk4 Golf era). Simple way to describe them to someone is that the Gamma IV says 'gamma' under the volume control & the Gamma V says 'GAMMA' on the cassette flap.
I seem to recall that I found the Gamma IV also came with orange backlight for Audis. But maybe it went under a different name...? (Symphony or something?) I suppose I must have a sales brochure for it somewhere to have seen that... :-/
There was a Beta - lower spec (just 2 speakers? not sure about the changer control, either).
Gamma IVs CAN take an aux input via a connector made up to fit the CD changer plug. Google for a how-to if you're handy with a soldering iron and just want a simple audio-in with no control from the head unit. Or you can buy one made up (L/R phono or 3.5mm) for about £30.
For a little more (starting at £50) you can get a CD changer emulator with an iPod connector which should let the changer controls on the head unit drive an iPod (skip track FWD/REV, and playlist access via disc buttons). You also get basic (track number) text on the Gamma's display. Later iPods need an adaptor to allow charging at the same time. I've just ordered the Connects2 kit (cable and charger widget) off eBay.... hoping it works....
Obviously, if you've got one of these gizmos in the changer socket on the Gamma, then you can't use the VW changer at the same time (6-disc, IIRC - and there were/are aftermarket cables to allow you to use non-OEM changers, but they were still pricey when I last checked in 2005-ish).
I think they came in late 1990s VWs - most CD changer emulator websites list it as being in the 1997 Passat, but I've noticed it listed for Golfs, Jettas and Polos. Not seen Corrado on any lists, but that doesn't mean much... most of the websites seem to have lifted the same text from somewhere.
There is a little red LED on the front - never lights up on mine, so I assume the Scirroco's neolithic harness doesn't drive it (although the car it's in has been subject to radio butchery in the past - I suppose I ought to try it in another one to see!) and I don't get speed-related volume control (if only!) - again, I think that's down to my wiring rather than the unit. I've read that they ID the car they are installed in and other stuff (CANBUS?) but it's beyond my ken.
There's a four digit code on them, hold down TP and TA until the display changes from 'CODE'. Each of the four digits can be entered by the 1-4 buttons (press each button repeatedly to increment; button 1=digit 1 and so on). If it says 'SAFE' you've exceeded the number of failed attempts, but as I recall you can just leave it powered for a few (?) hours and it'll let you try again. Have heard that they can lock completely if the wrong code is still entered after this stage, in which case they need some sort of intervention.
They remember their presets even when the power is off (never tried to find out if there's a limit on how long they remember them for).
Finally, lastly - IF ANYONE HAS THE INSTRUCTION MANUAL for a Gamma IV, I'd be really indebted to them if they'd let me have a copy! Dealer won't supply them (without the vehicle it came with) - presumably they still think that it's a nickable unit :)
