Have you done the experiment of bringing the Polks inside and connecting them with short cables and seeing how they sound like that?

It is true that you are going to hear more of the cable with lower impedance speakers than with higher impedance ones. But this is not the first place I'd look for trouble. 100 ft on 10 or 12 gauge is not unreasonable and the difference between 4 and 8 ohms is not that huge. Try the above experiment first.