Hi gftiv,
First, makes sure both TIU's are programmed into your remote. You can check which TIU addresses are in use several ways. One way is to start the process of adding a switch.
MENU / SYSTEM / SWITCH SETUP / ADD SWITCH
The screen will then display any TIU's currently in the system. If TIU 1 and TIU 2 are on the list you're OK. If one of them of missing you need to add it to the remote.
MENU / SYSTEM / TIU SETUP / ADD TIU
Once you know both TIU 1 and TIU 2 are in the remote you need to set them both to super mode.
MENU / SYSTEM / TIU SETUP / SUPER TIU
With both TIU's in super mode you can move back and forth between tracks and TIU's seamlessly.