there is an official alpine dealership close to where i live. the shop did the subwoofer box for me, and htey quoted me a price of 1600 euros for the alpine, im not sure if i want to pull the trigger on it yet, but i can tell you using aftermarket subs and amp on the oem head unit sucks. a lot of frequencies missing from the music.
pioneer also has one, its a smaller screen, more like the one our oem has, and it appears to be almost the same as the nex series. if this is true and it runs on nex software, it can be hacked. if you go to avic411.com (net?) you will find a lot of threads in which people hack the nex systems and install their own maps or what have you. i had the 8100 in my focus st and hacked it to run european maps. it was a bit of a pain in the ass but it worked flawlessly.
http://www.pioneer-car.eu/de/de/navgateevo
their trim is ugly though. one aggrivating thisn is none of these damn companies have trim to match the gti. wtf, theres tons of gti and gtd golfs here so why the hell not.