If i understand your question - your audience has an association with a knowledge domain. And your article type determines the domain in which the article exists.
Please try on a test environment...
1. Create a look-up relationship from Knowledge management.Knowledge Domain -> Knowledge management.Article type (Answer no to the relationship question).
2. Add the 'knowledge domain' attribute onto the Article type window.
3. *** copy rules can then be used to populate the correct domain as determined by selection made in article type. *** further explanation to follow...