In my experience, the problem using the 828 to generate CV has been a loss of linearity caused by impedence mis-matching. Making a very simple voltage following buffer with a cheap opamp for each output (or input) channel of your 828 should let you send sig~ out of your 828 with linear response.
i can recommend doepfer as a great company. if you have any questions, subscribe yourself to the doepfer A100 yahoo list.
dieter is up there himself and answers many questions, some other very knowledgeable people up there too, though I wouldn't expect them to have a lot of experience with max, but that doesn't seem necessary.