Kurs with and without Caen in MP

[Atelophobia]

Hi,

I bought the collection 3x times (2x for friends of course). The first problem: No connection possible althoug we forwarded the ports. The MP config in the game directory was of no help either.
So we had to intall hamachi ->
OK, we could go for a short test match.
Today I bought Caen and Steam downloaded it.
Now I wanted to play a Kurk basic map against a friend and I wan't able to join his server and he couldnt join mine.
A friend told me that you can't play with each other if both dont own the same DLC.
Now Im really mad. There isn't a way to disable the DLC afaik.
So how am I supposed to play against my friends?
The game is useless to me right now.