Thanks for the replies everyone!

I will have lots of wire left over from the spool of 4 conductor wire, so this is why I was asking whether I should combine the wires to "increase" the guage for the home theatre portion instead of buying even more cable. However, it doesn't sound like it will be necessary in my case. I guess if it came down to it, I could "double wire" the speakers since there'll be two wires just sitting there anyway.