Before spending the large amount it will take to acquire a more "premium" cable you might consider spending about $180 total to purchase two 18' runs of Canare 4s11 "Star Quad" speaker cable from Blue Jeans Cable. It ends up being 11 gauge as I remember. It has four individual 14 gauge conductors withing each jacket and two are combined within each spade or banana to result in 11 gauge per side.
If you end up not liking the cable you are only out a modest $ amount. You will find a good number of accolades and users here for the cable.