Okay, Craig pretty much had it right when he described what he understood the difference to be between the "composite TV" cable and the "RCA" cable, i.e. that the composite likely would be more heavily shielded and should be close to 75 ohms impedance(also note again that "RCA" is actually the name of the connector on the end, not the cable itself, so even the composite could be termed an "RCA cable"). For the short length involved and at audio frequencies the characteristic impedance of a cable isn't significant and if the shielding is heavier that might not be of audible benefit unless interference is heavy. But, as Peter said, since you have the more expensive cable you might as well use it.
