Elliot,
Hay buddy are you running DCS also or just TMCC/Legacy? If you are running DCS also simply connect the Legacy drop to the out Black Channels on the TIU and make sure you use the opposite outside rail for, your main Legacy drop. My Multi level layout runs perfectly using Marty F's technique for Legacy/DCS, I know your layout is a lot bigger, but it's worth a try.
PCRR/Dave