When I bought a new amp I switched from old 16-guage cable that had been around since the 70's, to new 12-guage cable. Not exactly expensive stuff, but there was a HUGE difference. I ran short so had the left front speaker set up using the new stuff, and the right front using the old cable. The left was noticably louder and clearer, to the point where after a day or so later I couldn't stand it and went out and bought the rest.

Maybe one of these days I'll upgrade to something even better...