If you choose to go with the custom cut length of RG-59 or RG-6, try to find something that is a "bare copper" center conductor, rather than "copper clad steel". It does a better job of carrying baseband signals, which is what you're talking about with the kind of LFE you would want to send to a subwoofer.
The large majority of RG-6 these days is copper clad steel, because it performs better in broadband signals. Low voltage installers use it all the time to wire digital cable, digital satellite, and cable modems.
In this case, though, you want to steer away from the copper clad steel and go with the bare copper.