Had a Connects2 box in mine before I upgraded, with an Auxiliary lead, fitted it myself without any real issues, only
problem I had was not having the cables I needed, and forgetting to put the earth cable somewhere! To clarify, the cable I was missing was the loom for the cd changer - this is what the box plugs into, fools the headunit into thinking it's the cd changer.
It fits behind the climate unit - just. I found the lead moved the headunit slightly so the drinks holder didn't pop out properly, didn't really bother me much. I just fed the cable down the centre console so it came out underneath the ash tray (there was a hole for the lighter wire, fed the cable through that). You'll need to drill a hole to the glovebox if you want the cable in there.