So, the question on the table is how a magnet which produces a magnetic field, not an electromagnetic wave, can influence the signal which is composed of photons that, if recall from Electricity 101, have no mass? Or have we kind of come to the conclusion that we actually don't care about how it all works as long as it works. LolGeoff raises a fair question, and a good one IMO. I believe I can shed some light on the answer, although my answer should not be interpreted as a defense of the efficacy of magnet-based tweaks, or as concurrence with Tom's statement that "magnets enhance the directionality of ac passing thru them much the same as cryo treatment of metals and conductors enhance and unify the direction of their molecules."
While as Geoff has indicated the speed of electron movement is VASTLY slower than the speed of signal/electromagnetic wave propagation, the two are intimately related. I believe the inter-relation will become clearer if it is thought of as follows:
Consider a signal voltage applied to one end of a cable, with the voltage applied to what we'll call the signal conductor being negative at a given instant, relative to the voltage applied at that instant to what we'll call the return conductor.
At that instant the applied voltage can be thought of as causing a VERY slow movement of electrons into the signal conductor, and a VERY slow movement of electrons out of the return conductor (at the source end). A VERY short time later DIFFERENT electrons will be caused to move at that same very slow speed out of the other end of the signal conductor (and into the load), while at that same instant still different electrons will be caused to move at that same very slow speed from the load into the return conductor.
The difference in time between when electrons slowly move into or out of the source end of the cable and when different electrons move into or out of the load end of the cable, in response to application of a given signal voltage, will correspond to the time it takes for the electromagnetic wave to propagate the length of the cable, which it does at a speed corresponding to something like 60% to 95% or so of the speed of light in a vacuum, the exact value depending in part on the dielectric constant of the insulation of the particular cable.
Thought of that way, despite the vast difference in speeds between electron movement and movement of the information-carrying electromagnetic wave, it does seem conceivable that the influence of a magnetic field on those electrons could also have some influence on the electromagnetic wave.
Regards,
-- Al