No need for the terminal cup in my opinion, just simply get some brass bolts, washers, and wings nuts from Lowes, and some trim rings for the speaker wire, drill the hole on the box, stick the bolt through the internal speaker wire ring, out of the box, and place the external speaker wire on the other end, and secure it with the wing nut. Much easier to install in my opinion, and a lot more secure, and easier on wiring.
Here's an example of mine