You might get at this by recording voltages with a two channel ADC. Measured at the amplifier speaker terminals, not at the other end of speaker cables.Changing the connections did not move the 150lb speakers.
If you think the differences were caused by background noise difference, or differing reflections due to me or some object having moved, or perhaps the mic temperature changed in the 15 minutes in between, or some other minor difference that is only subconscious in the recording, then you're saying these things are audible despite also being too weak to affect the frequency response (which is unchanged in every measurement), whereas separating the high and low crossover networks and drivers while and driving them essentially with half the output impedance is inaudible.
1. Biamping one speaker, measure HF and LF as a two channel recording
2. Driving one speaker normally (with LF and HF strapped together), and driving the other one with just HF or LF driven, measure the two amplifier outputs.
If both channels in the first recording are the same, and both channels of the 2nd recording are the same, then bi-amping is not doing anything.
Then you can think about whether the bi-wiring does anything...