If you are using the controller with the LUUDS, the o/p port does not come into play. It is the controller that listens for you to dial ** while connected to the door phone, which releases the strike.

So you could have as many door phones and controllers as you wanted, limited only by analog trunk ports.

(We have a site that went from a Partner II with 2 separate door phones and controllers to an IPO. They work MUCH better with a trunk connection, rather than a station connection. When the doorbox call is ended, the IPO does not give positive disconnect, and sometimes returned dial tone to the box until it times out)