rg6 cable will not work with speakers.

The sound controller is like the steering bars on a bike, and the speakers are the wheel: the controller is not just telling what sounds the speaker should make, it is the force that causes the speakers to make those sounds. The bars don't tell some component in the bike to turn the wheel, it turns the wheel itself. If the beam between the bar and the wheel receives metal-bending-twisting interference of some kind, your wheel will be unpredictability wobbly.

And you are right, you would likely not notice the difference because the power delivered to the speakers is high and the interference is so low, but if you are already dropping thousands of dollars into a sweet sound system, you would not buy unshielded cables that undoes all the unnoticeable differences your sweet sound system perfects.

And an expensive cable probably has a guarantee, great durability, is long, and has a brand name associated with it. And it sounds like to me, it's not 80$ for one cable, but for a set. I'm not familiar with high end cable prices.

But yeah, you'd never buy expensive cable unless an absolute beast (read: high end) of a sound system is your goal.