ok, so if cds and dvds get treated the same, then in the itemType column, set the value for both dvds and cds to the same, something like "media"
the idea is to have a common value that is used to tell the cart to apply the shipping rule.
in the shipping rule, you can then use this instead:
"Number Of Items with a specific Item Value"
If the Total number of items where "itemType" has a value of "media" is "<=" "2"