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Also, I deleted your duplicate post. You were under moderation since you added a link in your post and you are new here.
However, your ground cable SHOULD be the same thickness as your power wire so it's less strain on your amp. When you say your rear speakers are 10.5" are they subwoofers? How many do you have hooked up? Have you turned on the low pass filter if they are subs? Have you adjusted the gains properly? Those are some things to think about.