Bruce,
Thanks for your kind comments. I think your creative juices will be helped by looking at the patent for the MTH Z4000 and the unofficial schematic for the Lionel CW80 (both attached below) which have been previously posted by others in this forum. The Z4000, in particular, uses a novel method to convert the analog outputs of the throttle into a pulse width modulated signal to ultimately create a pseudo-sine wave output.
I believe the HiLetGo module can be modified and adapted to work with a variable DC control voltage from an external source. Before proffering a solution, I would have to bench test it. I think there are a few different approaches, including using a voltage-variable resistance, that could be used.
