Twl:
I disagree with your arrow directionality (i.e. "points in the direction of signal flow"). Analysis Plus tells the user to point the arrows of their ICs toward the preamp/control amp. Probably like you say, has something to do with the shielding and grounding.
However, I do not believe that cables are directional re: signal only. As the current flowing through an audio cable is AC, by definition, it flows in both directions, not in one direction as in DC.