Many of the Japanese SUTs (Luxman / AN:Kondo) use severe loading on the transformer to reflect back a small multiple of the internal impedance. This is typically applied to the SUT secondary and could explain this situation.
I think the key point here is much of the mystery and speculation around SUTs in general stems from the limited published data by the manufacturer.
The assumption of a 47kΩ terminating resistor falls out of the picture if there is a 5KΩ resistor internally soldered across the transformer secondary. This also mucks with all of the other assumptions/calculations.
dave

