Anyway, as an old audiophile, i’ve tried them all. The reasonably available anyway. I find that solid core copper cable (2,5mm2) brings a shine, a light in dark areas, a higher resolution, to the sound. Stranded cable sounds grainy, gray, matted etc. I guess part of the reason that Cardas, Litz etc dont market this kind of cable is that that it's too simple. Nothing fancy can be said or done about a simple solid wire. Did I mention that my cable cost about $1 pr metre, (30c pr ft)? Now I did. Not much profit potential in that.
I see that there are a lot of pseudo-metallurgists in this thread. I have nothing to contribute in that direction, and i dare to say that neither has most of these other contributors as well.
In other forums that i frequently visit, an assertion requires sources. A psysicist would indeed be very interested in the theories about the movement of electrons in and between the crystals of copper mentioned in this thread