It will be known as a CAN Gateway and will start with part number 1K0907530 - the letter on the end being the revision and you want 1K0907530L onwards should you go the OEM route.
Eddie-NL on here is the man to speak to, he could supply this at a much more reasonable rate and could assist as he is a top guy.
Don't count out the Zenec's, I see they constantly get slated for the price tag. Granted £830 is expensive considering they are getting more expensive with age due to the exchange rate. However I got one less than a year old from eBay Germany for almost half that, and you could get a brand new one for less than what you quoted - UK stores just import them anyway.
Don't forget it comes with integrated Parrot bluetooth, you don't have to change your CAN gateway, it has OEM wiring so goes off with ignition and shows navigation/track info/caller ID on the highline display and multifunction wheel if you have it.
Not only that it has excellent sound, connectivity (loads of RCA, reversing camera inputs etc) and if you have an ipod/iphone it can charge whilst playing music and video!
The Igo navigation is also very good - I have the very latest TeleAtlas maps on it and speed cameras, I've since retired my always updated TomTom.
I put some pics up here a while back
http://www.mk5golfgti.co.uk/forum/index.php/topic,43748.msg508087.html#msg508087You should try one before ruling it out, don't bother with the cheap Chinese ones as the menus on them make Ripspeed ones look classy.
I'm not saying this is the best stereo out there (honestly, I'm not!) but if you want 'bang for the buck' and as close to OEM as possible without buying RNS510 then this is one you want to consider.