I assume by "MOM" port you are referring to Momentary (as opposed to Mother 
). For your application that port can be left un-connected. Only the 2 wires need be connected to your opto-isolator.
The challenge in YOUR specific application is triggering the sound at 1V DC. With the hookup you are proposing, a 330 ohm resistor makes for a more sensitive trigger than a 470. It will trip at a slightly lower voltage. There are other issues described in the other thread with choice of power rating for this resistor but those are really secondary (easy to deal with). Again, it's getting the thing to trip at only 1V which is the trick. IF you already have the 470 resistor, then just hook it up and see if it works. Use the LTV opto-isolator; it is more sensitive than the one shown in your "factory" diagram.
