Sometimes you get lucky.
Class 6400 looks similar to its 'cousin' the Mak G1204, albeit the prototype 6400 class is a bit longer (1.4m) than your standard G1200 and is a diesel-electric rather than a diesel-hydraulic.
Sprog II was broken, the decoder was bad, etc... I ultimately discovered that the culprit once again was the decoder socket. So I removed the NEM651 socket and soldered the decoder directly to the pads. Problem solved.
The video at the top is a new one with just one locomotive (and a much slower pace than my last one!), the train the 6400 is pulling are the coal cars that I weathered in my last post as well.