Maybe this will help, simply put:
Paralleling conductors effectively creates 2 paths for current to flow equally, halfing resistance and increasing total conductor ampacity. The same length and awg size must be used. In a manufactured cable this is maintained by default.
Resistance Primer:
http://en.wikipedia.org/wiki/Electrical_resistivity_and_conductivityIf you work or live in a large building, the main distribution is fed from the utility transformer with no doubt at least one if not more paralleled "hots" per phase to decrease awg size while maintaining the ampacity rating of the circuit. Cost and ease of installation are improved big time. If you have 4 wires, it is of benefit to use all of them.
There will not be circulating currents... Unless you put your speakers in a jetted hot tub.
