Surprise! Things may have sorted themselves out a little tonight!
I went to the layout with the intent of taking pictures of the TIU, AIU and remote with message. Random choice as to which AUI and cable. The TIU is the Rev L with 6.1 firmware. Lo and behold, the connection worked! Don't ask me why, I have no clue. I connected everything the same as always.
So with the connection working, I decided to add the second AIU to the mix. Failure!
The second cable is marked with orange tape. I swapped connections, and only one AIU was found.
Running the unmarked cable to the second AIU was a success.
So at this point, I'm reasonably certain I have a bad AIU cable (the one with orange tape.) I ordered new cables and some adapters this morning, so I'll have to wait for them to arrive to finish testing. But things are looking up!
Chris
LVHR