Let's put it this way......its not the cables that make the system great its the overall collective effort of your equipment. If you have a $500.00 cable attached to a $200.00 system I betcha you won't hear the difference. Put $5000.00 cable on a $20,000 equipment you'll hear it. The difference sometimes is subtle so the question is are you willing to pay the big bucks for it......
I have tried doing AB's on different cables and I do hear the difference. One easy way to do an AB is not by sound but by sight. Get an elcheapo video cable and get one of a higher grade. If your player has 2 same video outs connect them both. Play a movie pause it at one scene switch it back (video 1, video 2) then see if notice any difference. Just did that to my friends TV last night and he did notice the difference.
Cables do make a difference but it has to be a collective effort between your system and your cables.