they can't spell.
It's not made of 39 AWG otherwise they would have advertised it as 11 AWG, and 588 x 40 AWG is not be 12 AWG.
Sound King is cheaper, go to parts express, buy what you need there, seperate the the two conductors and twist or braid them your self, use electrical tape to hold the twist.
Other smarter people may disagree, but I do not think the tinning will do anything for your sound. The company probably just bought several thousand feet of wire left over from someone else's run - that's why it's tinned.