2 sides to this:
#1 the Protosound 1 based electronics and firmware inside the loco (Trolley/Subway) are ALWAYS only controlled by conventional varying of voltage on the track and traditional bell and whistle DC offsets within the track power. Again, as an interface limitation- these require "analog" conventional control methods.
#2 The TIU has 2 outputs that are possible to use as variable outputs that can perform conventional control, vary the AC output track voltage, and also apply DC bell and whistle offsets within basic function we know as "conventional control".
So, you would have to ensure you are using the variable channel wired to your track and power source, and have that configured.
The DCS manual then covers what more advanced functions under conventional you can access.
https://mthtrains.com/sites/de...ction/20as14017i.pdf
Specifically chapter 8 starting at page 99
Also, page 114 and 115 cover conventional operation details.
