Set your variable channels to fixed. It's also explained in Barry's book. Been a long time since I did this or I would provide more details, but you may have to set the voltage to 18 volts too, sorry, I can't remember exactly without digging out Barry's book.
Not sure how you have your Legacy control wire connected, but I have mine connected to ALL commons on my TIU outputs. You just have to make sure the Legacy signal gets to the tracks on your new electrical district.