Use 12ga cable. You have no problem running them side by side. Hell, they come out of your amp close together. If you biwire, you would run them together. There is no problem. Use the shortest lengths you can to minimize loss. Even the surrounds, with 1 being 10ft and the other being 40ft will not be a problem as long as you use a 12ga cable. If you are really worried, go to a 10ga or an 8ga cable (providing you can get banana plugs or spade lugs to fit them) and then there will definitely not be a problem.

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