Given the new information I agree with @gdaddy1. I would set the system up without the subwoofer running the speakers full range.
If you use the system for video also you could try the subwoofer via the RCA input when doing so. Value of this approach would depend on how low one can set the subwoofer crossover. Set the crossover to lowest setting. You would likely find yourself sub turning the subwoofer off for music, maybe not using it at all..