In other words, is it necessary to use two different items from a set in order to get the bonus?
For example, here is the Hallowed Avenger hand crossbow from the Hallowed Armaments set. Since it is a hand crossbow, it is only usable by demon hunters. The only other non-class specific items in the set are a shield and an axe. It seems odd to me that if you plan on using the Hallowed Avenger, you would need to pair it with a shield or axe to get the bonus. Can you use two Hallowed Avengers and get the bonus?