Cable Direction

Toward the speakers.

If your cables have arrows then you should always have them "pointed" in the direction the audio signal is travelling. Source >>> Preamp >>> Amp >>> Speakers

Whether or not it makes a difference is another can of worms...

Are they Nordost cables? Nordost arrows should point at the source of the signal, not the destination.

Just to clarify, the current is AC, or Alternating Current, so it goes both ways. Therefore it is better to think of the directionality in terms of a "source" and a "load". In a metrology (calibration) lab, the shield of a cable is usually only connected at the source end in order to prevent ground loops (I'm simplifying this a little). The arrows on the cable should be pointing toward the load, which in the case of a pre-amp to power-amp connection would be the power-amp.