John, on your first suggestion to try it both ways, there might be a problem. If there's a polarised capacitor for the high-pass filter, connecting it backwards can cause it to explode. If the enclosure was opened, the presence of the filter(which would also have a directional indication if polarised)connected to one of the terminals would answer the question.
As to what you suspect about that actually being the back of the sub, I tend to agree(by about a 60/40 margin). Looking at the picture I linked from the earlier thread, the "right" terminals are shown to the left. This would seem to be illogical(requiring the wiring to the mains to cross over each other)unless that was intended to be the back and it would then actually lead toward the right main.
