a problem with headphone swapping is that even sequential serial production headphones may not have basic driver sensitivity matching to 0.1 dB - which level difference CAN be heard in ABX DBT testing
also the uncertainty in placement position, differences in seal if you have hair likely would mean even "perfectly" matched headphones would differ by more than the DBT threshold for repeated (re)placements - requiring many trials to give statistical resolving power
the engineering approach is much simpler - a fundamental of the Scientific/Rationalist Physicalism/Materialism world view is that the "same" (within limits of measurement noise) signals at the headphone driver terminals then the headphone produces the "same" (again within noise, environmental, parameter drift of the transducers) sound
with a modified headphone you could measure the V at the driver terminals with different cables attached with a "prosumer" grade soundcard w good ADC, DAC and
http://www.libinst.com/Audio%20DiffMaker.htm
you can then listen to the difference file itself - and even turn the gain up, add the amplified difference track to the "reference" recording and try ABX in foobar with whatever "high resolving" system you lilke - even post the files for others to ABX
for typical cable and headphone parameters there will be measurable differences with headphones that have large impedance bumps - like the HD600, but comparing with ABX thresholds they will be orders of magnitude less than established statisically significant audible frequency response variations:
http://home.provide.net/~djcarlst/abx_crit.htm
of course you simply can't convince "true believers" that a 24/192K ~US$130 ESI Juli@ card is by all engineering measures "more resolving"/accurate at audio than a $13K STOA turntable, hand crafted cartridge