OK, back:
My first hifiman can was a used HE-500 with the stock cable reterminated by me to balanced. I got used to the sound for what - 6-8 months (you know "broken in ears" and all that). Then I bought a used (originally sold in Japan) HE5-LE with two cables, the stock one and an old Black Dragon v1 which I knew was some sort of high end brand. They both had the old style conmnectors, so I tried that Black Dragon v1 vs stock silver plate HE-500 cable. Instantly obvious differences. BD had less ringing/splash in the treble, and a very menacing but musical way with bass under 40 Hz. I got the wife to change the cables, and asked her to toss a coin to come up with the order, to listen, then I wore a thick towel so I couldn't ID them by touch/weight. Same thing, called it right 6 for 6.
Then went back to the HE5-LE. No test needed, in that case the mids were also much better, it could be the stock cable is shot, it sounded worse than the other HFM stock cables I have experienced (HE-6, HE-5se, MD-4XX).
I bought myself a HEX v2 with stock and artic cardas cables - both terminated in balanced. Not the same size as the old HFM. Again the differences were not subtle. Due to the word on the headphone I decided to try a silver cable (used Ted Allen litz). Again it killed the stock, but it was close with the copper Artic. Given I knew that silver was "supposed" to be better, I could have been influenced, so thats a draw.
Finally, the HE6se, went ahead and bought a new but cheap (by high end standards) cable from Custom Cables (UK). Another wipe out of the stock. And I repeated the towel text 6 times and was 100%.
I purchased a custom cable for my HD-600 balanced and its better than the stock SE, but my amp is much more potent into balanced, so that's a no call. Had a LCD-2 for a short period and the two cables I had sounded the same.
Been using the same amp power cord for 26 years, and the 5-6 it got tossed against over the years didn't outdo it including a ridiculous 5 foot for $5000.00 cretinous one I ran into back when.
Used the same speaker cables for 20 years at one point - DIY.
Use the same Belden balanced interconnects for about 20 years. Now SE, yup hear a lot of variation with those, but why bother? When you can get quieter and cheaper?
I'm not your basic everything matters guy, but I'm not the other guy either. Ears and mind open here - as well as humanely possible.
I'd be happy to replay the HE-500 or HE-6se tests on my gear - easy money, and stick the 'X' in ABX where the sun doesn't shine.