Ranger,
there's absolutely nothing wrong with RG6 for a sub. Since RG6 was developed for the purpose of getting video and antenna signals from one place to another, and the quad shield's purpose is to make double double sure that the cable doesn't pick up RF interference, it's just not what you'd expect someone to choose for an audio wire. The fact that the common connector for it is an F connector makes it not the best choice for audio. But that's for reasons of how you use it and what limits it places on you. It's not because the cable can't properly transfer the signal.

We've had a discussion here in the past as to whether it's okay to use RG6 for audio. That was started by someone who had only used cable designed for audio. It's a good question because it's good to know the capabilities and limits of the things we use. That way, if we have some strangely limited circumstance, we'll be able to think our way out of what looks like a problem.

I've told here about an excellent cable installer who was trained to NEVER use an F81. He was told that an F81 lowers an RF signal by something like 3 dB. So, sure, he always ran a new cable if what he had was too short. But I explained what 3dB meant in terms of power, and then I stacked up six F81s and showed him with a signal meter that the total loss was only a bit more than one dB.

See, he had not been taught to know all about and understand what he was doing. He had been taught in a way that made him afraid to do anything that varied from the instructions he was given.

Life isn't like that. We often have to use things not designed for the purposes at hand.