You may have a very difficult time getting 8/9 Ga wires. I have seen some 10 Ga, one of them being Clarity Cable. Dana cables has a ridiculously low Ga. but nowhere near your price.
The problem is that when you get to that point in total gauge you have a horrid time putting terminations on the cable.
There is another solution; double up the speaker cables. Simply parallel two of them vs. one. It passes my Law of Efficacy, and I use that method whenever possible. So, don't sweat the total gauge, when you can double cables and get similar effect.
Finally, I'm sure there will be plenty of naysayers, who likely haven't tried it but will carp on and on about how it "shouldn't" work. I'm not interested in arguing my methods; I use them because they do work, and work quite well. :)