@SolomonHenry, I'm sorry but nothing has changed and it is still a duplicate of your first question which has the solution to the question asked, I know since i personally answered it and is your 3rd question in the same subject. So i see know reason to reopen it.
@kaiser its not quite simple as chained selection, he is asking for a way to filter the 3rd dropdown with only terms that have a post in the previous (2nd) dropdown selection when the 3rd and the second dropdowns are different taxonomies.