If one is going to ever run conventional, one must set up TIU tracks per the DCS instructions. If one is only going to run DCS, one might as well set the VARIABLES to FIXED. If one is only going to run conventional occasionally, you might as well set the VARIABLES TO FIXED since, if you want to run conventional, merely moving the thumbwheel when TRK has been pressed will convert to VARIABLE for the session or until emergency stop is pressed, bit it is not necessary. If one runs conventional often, or ever leaves conventional locos on the track, I wouldn't set the channels to FIXED because that can have unpleasant consequences (speedy takeoff) if one has to repower up, such as after an emergency stop. When set to VARIABLE, nothing will move until you move the thumbwheel one notch. When I turn on layout power, within a few seconds VARIABLE channels set to FIXED power up to full voltage. If I have an old Lionel E-unit loco on the tracks, there's a 50-50 chance it will take off flying. This has also happened to me with a PS3, which for some reason locked itself into reverse, requiring a conventional reset to cure.
I am trying to think of what problems require channels to be set to FIXED to diagnose.
