Hi Ian - thanks so much for your detailed posts in response to my questions about your comparative cable testing. It sounds like you and your friend have gone to great lengths to study these effects by ear. Am I correctly understanding that you think he may still have some or all of this data available, in the form of the recordings you made? If so, and if there is a way to compare, chart and graph it, you might be in a pretty unique position in terms of shedding some light on the great cable debate. If it is possible, and if you ever have a chance to publish this in some form, I know a lot of us cable agnostics would love to see it. (Maybe I just spent too much time reading Hume as an undergrad (thus the handle), but absent measurements, I just see post-purchase justification phenomena and/or confirmation bias as better explanations for perceived changes, as compared to audible improvements based on headphone cables. Factors you pointed out, like earwax, one ear possibly being better than the other, atmospheric pressure, low level background noise etc. only further complicate matters.)
Also, thank you for clarifying that there is no issue in so far as ports are concerned with respect to direct wiring. I hadn't realized that the connectors were sealed off. I do wonder about possible vibrations though from the new hardware you installed. Sennheiser used several patented plastics in the housing of these headphones to eliminate resonances and vibrations. Introducing metal fixtures into the equation in order to secure the silver wires seems as though it might have its own problems. Thoughts?
Honestly, there is no more debate in my mind. I could hear cable differences from the outset, but as my setup has improved, these differences have only become more pronounced. It has gotten to the point where I can easily point out which cable material is being used on my HD800s and HE6s blind. 10/10 times.
The trick is to learn the sound of the cable so you know what to look for in comparison to other cables.
Crucially, I have found cable differences to be far clearer when switching materials. Almost every aftermarket copper cable of decent quality I've tried sounds nearly identical, and produces nearly identical improvements over mediocre stock cords. It's when I switch from copper to silver or vice versa that I can really pick out variations reliably and consistently. IME, wire material has the greatest effect on its sound. More than geometry, gauge etc.