The main difference besides the built-in wifi is they removed one white per puck and added an extra blue. Also, you get the ability to run channels over 100% intensity on the HDs. Each channel has a specific maximum over 100% you can run it, but within that boundary it depends on what you run each channel at and the overall power you are currently using. (Maybe you don't run whites high, but want blues higher over 100%, etc.)
The director will not work with the new HDs either, you have to use the built-in wifi control. It works ok, but IMO, the director was a better control module, especially with multiple units.