Yeah yeah experts say this and that, and heresay says this and that. The bottom line is that cable business is entirely headphone-dependent, it depends on how revealing the headphone is. On a Beats Studio you won't hear any difference between silver and copper cabling of course because the headphones overshadow any subtle difference.
On more appropriate cans it's fairly well-known in that pure copper sounds warmer, with a looser more rumbly bass and less prominent treble; vise versa for pure silver. Silver-plated copper tends to be something in the middle.
On my HE400, the difference between Hifiman copper and Hifiman SPC is subtle but my ears picked it up right away; my HE500 reveal much more significant tonal differences. I can imagine this difference being even more apparent with something more ultra-revealing such as HE6 or HD800.
........and SPC/silver maybe better at instrument separation ? Yes, SPC might be safe middle ground actually.
I just got a good deal on these cans so I'm going to try them for a while and if they are not for me go for modded Fostex.
So happy to join the Hifiman-HE400 tribe anyway !