Has anybody tried using single solid core cables?

Try hooking your cables up backwards...all hell breaks loose, the cat explodes, and music becomes an unlistenable heap of cacophony rendering the listener on the floor curled into the fetal position wimpering, "stop, please stop."

No one has mentioned that the insulator or dialectic material is as important as the conductor.

I purchased couple of feet of 16 awg, OCC copper, SOLID CORE, Neotech hook up wire with Teflon jacket from Parts Connexion and silk tubing to conduct an experiment on my Cronus Magnum.

The cronus uses pvc jacketed, multi-stranded wire throughout the amp's power distribution. I switched the wires going from the IEC inlet to the fuse and from the fuse to the amp's circuit board with the newly purchased, teflon jacketed, solid core, Neotech wire. There was no doubt that the sound had changed when I first listened with the new wire. The teflon tremendously colored the sound. All natural dynamics and tonality that I previously had was lost. The sound stage shrunk in width and extended deeper in depth. The imaging gained focus and layering. Teflon caps have a burn in period of 450 hours but there was no way I could wait that long for these cables to "burn in".

I listened with the teflon wire for a week then I stripped off the teflon and replaced it with the silk tubing. Again, there was an immediate change in sound. The OEM sound returned. The original naturalness and dynamics was present. I decided to leave the wire alone and I did not listen to the stock wire vs. the silk insulated solid core wire.

Keep in mind that these differences were noticed from wire that wasn't even in the signal path.

For those of you who heard differences in solid core vs. multi-stranded wires: were the insulators made of identical materials between the 2 types of wires?

A comment on a quick method of "what is the gauge of TWO of the same wires"..
Generally in the audio use range two same gauge wires add upto the third less gauge number.
So two 25 gauge wires equal one 22 gauge wire
Two 22 gauge wires equal one 19 gauge wire
Two 19 gauge wires equal one 16 gauge wire..

Two 15 gauge wires equal one 12 gauge wire.

FOUR 25 gauge wires would then be like one 19 gauge wire...

This is for same types.. Solid core, to solid core etc.
As Almarg used the tables for the resistance and ampacity give this generalized result. easy to use.

I just switched from stranded #10 carol wire to #12 solid core for some power cables.
There is a difference.
The carol stranded had a big robust sound.

The solid core had more inner detail,I noticed little things that were buried with the stranded.

I am sticking with the smooth but detailed sound of the solid core.

Solid core copper and stranded copper do not sound the same.
Solid core DIY speaker wire had less bass but the treble and mids were much more defined and less tizzy.
I could always hear a difference when I used each type of wire as DIY bypass fuses.

The solid core DIY fuse was less harsh than the stranded.

I no longer use DIY fuse bypass devices, as there are replacements for the stock fuses today.

Yes, I have experimented with solid core copper and solid core silver cables. The sound is unnatural, but it can make vocals sound better than they are.