Balanced cables.
I'm not a fan for 2 - channel audio. They work great in pro audio where there are 100' - 200' runs or for undersea communication cables.
Like Steve said, the additional components, doubled capacitance and generally crappy, high mass connectors with ferrous screws and inferior dielectrics add up and take their toll.
Give me a pair of low mass RCA connectors, high purity wire (pick your metals), good solder and very little of it... combined with an intelligent lay. That is the recipe for superior interconnects.
More than once I have taken a balanced piece of gear, removed the connectors, gone in, bridged the ground and cold and taken an unbalanced connection out. That ALWAYS sounded better.
There is no magic involved in superior SQ. It all boils down to intelligent design, proper materials selection, a great lay scheme and excellent execution.