What speaker wire gauge are you using? As per my limited knowledge, wires heat up if the wire draws a large current the wire gauge cannot sustain. This is rather strange for a speaker cable to even burn the terminals. There could be a near-short condition at the speaker end. Not shorted enough to trigger the protection circuit, but almost (very low resistance) to draw current the wires cannot sustain. But it's also possible the surround channels do not have speaker protection, just the fronts. Change the wires to a higher gauge. But it's still odd because even a thin gauge 18 can still do the job unless you listen at very high volumes. But even so, surround channels are rarely visited with loud ambient audio information to draw enough current to burn the terminals. And check if there's a shorted on the terminals of the receiver and speaker sides.
