I guess I'm a little late to this party, but I don't see how you connect the Lionel Legacy Base and the WIU to share the TIU RS-232 Serial Port? Nowhere in the Addendum is the WIU even pictured. What cable or combination of cables do we use for that?
Pictured below is my 14 year collection of cables. The top one worked well to run TMCC Cab-1 with DCS back in the day. The bottom cable was supposed to let Cab-1 and Legacy play with DCS but I could never get it to work properly. I could not run TMCC trains with my DCS remote using the Legacy for TMCC control.