Adding a third keypad to a Caddx NX-8, wiring help requested!

["brim" <bcruze@xxxxxxxxx>]

I have a perfectly working Caddx NX-8 system with two keypads that I'd
like to add a third keypad to and I have a question about the wiring.
This system came installed with my house but I think I have the wiring
figured out.  Both keypads are wired directly back to the NX-8 board.
Now, I'm assuming I could add the third keypad's wiring back to the
board but it would be much easier for me to tap into one of the
existing keypad's wiring.

Is it possible for these keypads to be wired in series (the
wiring diagram in the manual seems to suggest so)?  Or will I have to
run a separate wire bbck to the panel?  Thanks for your help!