That really depends on the length of the runs from AVR to the speaker.
For short runs under 15' 16gauge is OK. For larger runs up to around 30' 14gauge.
I wouldn't mess around and just go straight to 12 gauge.
Don't bother with $10 a foot fancy scmancy brand names promising ethereal sound clarity.
Go to any big box home improvement place and get the low voltage outdoor stranded 2 conductor 12 gauge black sheath wire. Its about .65 per foot, and works great unless you are running over 250 watts per channel, at a distance of 100' or greater.
After extensive research, I ordered 12 gauge. I was about to braid twist and whatever else to have the perfect wires but when the rubber hit the road I was just spinning my wheels. If you are going in wall you might want to go with in wall wire. Otherwise grab whatever is cheap.
16- or 14- gauge speaker wire is more than adequate for most bonus room surround systems. Of the thousands of systems I've installed, I bet 12-gauge wire would have made sense in less than .5% of them. The OP may have a theater in a box for all we know.
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