Hooking my 2 main towers from a 7.1.2 surround sound receiver?

There will be a slight improvement in output to the remaining speakers...A lot depends on what AV receiver you have and how its wired but in most consumer grade receivers even if each channel is labeled as discrete they still share many components between channels the power transformer for one which will not have to work as hard...The difference will be slight though as most of the time you are not playing your AV receiver to full capacity anyway a lot depends on what AV receiver you have and how difficult a load the speakers you have present themselves to the amp...and also the volume you play your system at on a regular basis but at least theoretically their should be some improvement in output and also less distortion....

Update 2 Take a look at Blue Jean cables high quality at reasonable prices....also Steren RCA cables...really good at a discount price...