10 gauge is plenty for that power for speaker wire. Coulda gotten away with 12, possibly 14 //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif.
I like 10 gauge and use it for just about everything, be it 500w or 3kw //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif.