Hello people! My first post! a bit nervous, but here goes!

Just bought my first car! very excited, and happy! an Audi A3, 2008 mod. And my big question, is;

I want to change the navigation/sound system in the car, to a newer model.
I have been looking at this one;

7" TFT Car DVD Player GPS Navigation 4G SD AU Asia Africa Map for Audi A3 | eBay

(or one like this)

The original one;

(http://www.ebay.com/itm/AUDI-A3-8P-Original-Navi-Navigation-1-MP3-Navigationssystem-BNS-5-0-8P0035193E-/251374425621?pt=Technik_Auto_Hi_Fi_Navigation_Einbau_Navigationssysteme&hash=item3a87155615)

But how do I know that it will fit? I do not believe its a Bose system from before. so how do I know it will fit? and that I can use it?

Any help is muchmuch appreciated!

Kind regards, Audi newbie