Speaker cables can make a HUGE difference. I custom make my own speaker cables and when I took them to a friend's house, whose system is WAY better than mine. the difference was so huge that he traded me a Butler Audio 2250 stereo amp ($3000 new) for one set of my speaker cables and one set of my interconnects. They made that much difference. Of course there is no one perfect cable for all system, but for his Martin Logan SL3's they are heaven.
I'm not saying this to sell cables - I make them for fun right now - but only to emphasize that changing cables is kind of like tube swapping. They all make a system sound different. And since there is no such thing as perfect music reproduction, all we can do is decide what kind of distortion (change from the "original" signal) we like, and go from there.
Thanks, and happy listening!
Gary