We have test equipment that can measure small differences in impedance and no they are not inexpensive. My inquiry is not so much about the impedance of PCs but rather is there measurable difference in the quality of the plus and minus dc power rails of the end equipment or a measurable difference in the ac line (EMI) due between stock and aftermarket PC cables (looking in or looking out relative to the end equipment). At this point, I don't even want to say whether or not it makes an audible difference. I just want to know if it makes a measurable difference. If you can see that there is a measurable change in noise / ripple / EMI ( or some other quality ) then it follows that you (may or may not) be able to hear it. I think it would be interesting to do a comparison between a stock cable and an aftermarket cable under controlled conditions. I am an EE that has worked in power for many years (disclaimer, not ac but dc/dc converters). If there is an audible difference, there should be a measurable difference ( and yes I agree that it may be possible that we don't know how to measure that difference yet ). Anyway , it would be interesting to me at least to look at the obvious characteristics like conducted EMI and PSRR. Those differences would be easily explainable. If there is anyone in the DFW area that is interested in doing some real (and unbaised) testing let me know.