Uplink's documentation for the 2500EZ isn't up to par just yet. The one they do have doesn't show a serial interface for the 2500EZ, nor does it state such in the dealer sheets. From my experiences, once you configure the serial interface, it essentially overrides the majority of the dip settings, not to mention if you don't land any wires there, it's not going to make a difference.
I would ask Uplink as to the proper orientation of the plug, it's their product. The DB9 is pretty self-explanitory.