Checking if monitor speakers are out-of-phase?

Oh, swapped the wires in the molex connectors. That works and was probably the easiest option out of your choices.

Yes, an extremely unlikely problem. Good final result though.

The DSP is used to pull the frequency graph to a straight line. So, yes, that would mean it's always in the signal path. I couldn't find anything about an "off" or "bypass DSP" switch in the software. Of course, not having the monitors and not spending hours on it, makes this a bit uncertain.