Now you know why many of us fellow simmers are greatly indebted to the very talented and knowledgeable individuals who have spent their own time in providing us with their GTN 750 modification for Carenado aircraft equipped with the Proline system.. 

Alright, so I went to see what it said about the navigraph extension pack and it was clear to me that it's something I had to buy to get vnv to work. So I bought it (it was fairly cheap) and now the VNV button is working and I got altitude settings for each waypoint in the flight plan page (as shown in the picture from FS Mania). It's not the latest AIRAC but it got me the other features anyway and I did read somewhere that updating it to the latest AIRAC might cause the game to CTD so I will probably stay away from updating it for now. I must say it's a really nice plane, but damn, the instructions and manuals from Carenado arent particulary helpful... :P Thanks all! :-)