thanks for the answer, i am crossposting allready, to try to spread the information everywhere as good as possible.
I think there is a project ongoing called fpgaSID and lately they are doing pretty good progress.
In the link above you will find further information.
From what i have seen, it is open source and he is currently getting good along with the filter implamantation.
Andi6510 is one of the gents behind it: http://www.forum64.de/index.php?user/9610-andi6510/
It might be worth contacting him...