I'd have to say that your both right in your own ways.
Technically, blueflamed03 is right. Higher amounts of smaller strands will carry more current AC or DC than lower amounts of bigger strands in the same cable size. This is due to surface area or air gap. Bigger strands have more air gaps around the strands than more smaller strands, so higher strand count carries more current. Fine.
But
Sir-Lancelot is also correct when he says, who cares? This original post was for a big three upgrade. In a big 3 upgrade, where your only dealing with 105amps OEM, maybe more if you upgrade the ALT. It doesn't matter that you bought top of the line wiring. The truck's wiring doesn't come anywhere even close to maxing out the current handling of welding wire. You blew your money on nothing.
Car audio? again blueflamed03 is probably right. High end amps may draw peak power sometimes. To get the max performance out of the amp on competition day, you would want the extra current capacity of the higher strand count wire. But we are talking high end amps. Most consumer grade stuff, IMO you wouldn't hear the difference. And you certainly wouldn't need higher strand count wires when just cruising around or daily driving.
It's kinda like buying gold-plated usb cables for your printer. WTF? It's all marketing and peer pressure, and I gotta have that bling! I gotta have those gold plated cables!!! Maybe even with a voltage meter! Even though technically gold plated conductors may transfer current better than a tin alloy...so what?...Your printer doesn't print any faster.....
At the end of the day, I'd buy welding cables for the big 3.
/rant