Has anybody tried using single solid core cables?

Another + for the Clear Day Double Shotgun speaker cables.
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I'm not sure why cables have to be thick since speaker source impedance for back EMF is mostly resistive but it will lower inductance of straight wire. Skin effect starts at gauge 18 in copper at 20kHz. Stranding wires will make it worse because current will flow toward outside jumping from strand to strand thru impurities while skin effect still exists. Better solution is to use insulated strands. Placing them in regular fashion puts them in magnetic field of each other still allowing some skin effect. Better solution is to place them either on hollow tube (like in Indigo) or as a tape so that each strand is only in magnetic field of neighboring strands. I don't know what is audible and what is not but Indigo was great improvement over thick stranded Monster Cable (that was plain horrible). Later I found Indigo to be thin sounding and replaced it with Acoustic Zen Satori Shotgun that I will likely keep forever. It is total of gauge 6 and I have no idea why.

Jea48, am I missing something here? The Indigo diagram at the link you
provided seems to show 8 strands of 17, 19, & 21 gauge solid copper conductors
per cable. Not a single solid conductor that the OP seemed to be interested in.
This might explain their description of Indigo as being stranded. I guess the less
desirable alternative would have been if the individual conductors themselves
had been stranded rather than solid. Have to say the number of cable offerings
from AudioQuest (current and archived) really has me scratching my head.
Could all those offerings really represent significant technical/sonic differences?

Solid core singular conductors is why I prefer Cabledyne cables. They are also available in copper or silver wire. I have always found multiple or stranded conductor cables to sound phasey in the mid-high range.