Are audio cables directional?

Yes, there does seem to be a directional influences on the fidelity of transmission. This includes single-ended transmission as well as balanced. All conductors and transmission formats Zu has experimented with, from metals to rocks, exhibit directionality and signal fidelity changes. There are influences of the conductor structure and there are influences of the insulators which means that nearly all wires or cables will sound better in one direction or another. In some, direction can be reversed, others can’t. Some are the result of design and implementation, like grounding shield at only the load end, others are the net result of signal propagation. Please read the “Burn-in” for more on the how and why, much of what is discussed there relates to cable directionality.