Ron, welcome. You don't specifically identify your receiver and sub and the question isn't entirely clear. I'm fairly familiar with Onkyo receivers and I'm not aware of any that have balanced outputs. If it is, a balanced output sends out two voltages(of opposite polarity)rather than one, which results in a 6dB stronger output compared to the single voltage on an unbalanced coaxial cable connection. The balanced input then adds the two voltages after correcting the polarity, but reduces gain by 6dB so that the overall level is the same between inputs. This has an advantage of greater resistance to outside interference, but it isn't really significant in most home environments.
I'm wondering if maybe the terminology hasn't gotten a bit tangled-up here, since you also mention "speaker cables", which have nothing to do with the rest of the question. It would be helpful if you added more details.
