As mustangcoupe indicated, those speakers are the right ones; they are inexpensive and very low ohms so you can run a whole bunch of them if you want. They're sorta plastic-welded to the faceplate, so you just break it off - and the mounting holes hook right up.
Of course, they work best in the flush-mount box which is sold separately, but makes for a much cleaner look... I have 3 in my house.
Just remember to wire accordingly; though we've heard of people successfully using the unused pairs off the cat5, but I personally ran something better - I did 18/2 though I'm sure I could've used lighter gauge.
I personally love it - when you're working at a keypad, your feedback comes from the point where you're working; not from a speaker in some central spot across the house. If you use keypads all over like I do, you get very balanced audio throughout the home.