The problem is even if you can prove there is a difference in the electrical waveforms caused by the cables (which is very doable and a project im working on now), it is near impossible to show that they will cause an audible difference in a quantitative way. My percolations on that subject brought about one idea, the headroom listening head and sealed audio chamber. Basically the constants would be amp, dac, pulse generator, grapher, the head, the headphones would have to be broken in thoroughly, plugs etc, and independant variable would be changing out the interconnect between amp and dac at a length of 3 meters using both the frequency response graph and also a sound spectrum analyzer (or something cool like that, maybe a super sensitive oscilloscope?) and see how they reproduce each wave with different interconnects. Thats just my .02
Dave