There's no such thing as a DivX codec specifically for Magix. This might be a misconception. A codec as a codec. I mean, there are different systems and technologies (in this case DirectShow compliant codecs), but there's nothing like a special DivX codec for Magix. However, if you install the DivX codec from the official website, the Magix video products will be able to utilize it for import and export.
But how do you tell Magix which codec to use? At present I'm stuck with the infuriating Main Concepts codec which decides to splatter its ugly logo all over the screen when I import an AVI file.
I can't see where you can "tell" Magix to use another codec....