A friend of mine has purchased the Onkyo S655 HTiB and needs to run a long subwoofer cable through the attic to the sub that has to be located behind the couch due to the WAF. This could possibly require 40'-50' of cable. He is on a budget and a local Tweeter manager suggested that he could use a solid core coaxial cable such as RG-6u. Would this compromise the signal reaching the sub and consequently the sound? Has anybody tried anything similar?