To bi-wire or not to bi-wire?

Musicnoise...Your statements about lack of HF hearing are correct, but the conclusion, that HF response of an audio system is unimportant is not correct. Hearing tests for frequency response are done using sine waves. I can't hear a 14KHz sine wave, but I can detect when music is limited to 14KHz. (14 KHz was a while ago and it is probably worse now). In seeking an explanation I have come to believe that the ear senses, not only pressure change, but also the rate of change. This would correspond to steepness of the sound wavefront. A 14KHz tone that is not a sine wave can have a wavefront steepness corresponding to a 20 KHz sine wave. I haven't tried it lately, but supertweeters with response to 40 KHz and higher are audible to some people.

Musicnoise - with normal hearing, one can hear intensities from 0 dB to 140 dB. This corresponds to power ratio (defined as ratio of the highest audible intensity to the lowest audible intensity) equal to 100,000,000,000,000 - I would call it incredible range. Often structures cannot sustain sound levels and vibrations at 140dB SPL that we can.

This would correspond to steepness of the sound wavefront. A 14KHz tone that is not a sine wave can have a wavefront steepness corresponding to a 20 KHz sine wave. I haven't tried it lately, but supertweeters with response to 40 KHz and higher are audible to some people

Given that the ear drum is a filter that removes high frequencies from the inner ear it is hard to believe that anything above 20 Khz has any bearing at all in an adult. Test have never shown people able to hear at 40 Khz. So whatever they are hearing it is most likely an artifact that is in the band of 20 Hz to 15 KHZ and most likely something around 500 to 5 Khz where our hearing is most discerning.

Once again, like with amplifiers flat to 200 KHz - it seems plausible that the increased bandwidth of certain designs might cause differences to appear in the audible spectrum (amp instability at HF perhaps causing in band artifacts).

Alternatively, band limited devices - such as the use of a metal/ceramic transducers that are band limited and undamped and therefore have ringing problems within the audible range (requires a sharp high Q filter to prevent ringing) might cause phase distortion in the audible range. Like the brick wall filters in early CD's - it was known that the severe high frequency filtering sometimes caused audible artifacts/problems in band. In that sense, a device that has greater bandwidth might have better in band response - due to less artifacts from sharp filters...

In essence, there might be audible differences but the audible differences are most likely in band. This is the way ATC Hypersound technology works....modulated ultrasonic frequencies react with non-linear air particles and produce audible sound - again some mechanism is required ( in this case non linearities in air at 110 db SPL at ultra high frequencies) to make the effect audible. Perhaps a blind or something in your room could act as the non-linear converter.

Musicnoise - with normal hearing, one can hear intensities from 0 dB to 140 dB

Agreed. And how most home systems can be called "Hi-fidelity" when they are limited to maximum SPL of 95 db SPL at the listening position (before compression distortion and other non linearities appear in spades)....well lets just say that is a much bigger mystery than bi-wiring!