Hi well its not 100% solid proof but its the same sort of test I have done several times with a similar result - ie swop a wire round and see if sounded different
I posted a link to this video in the USB cable thread and not a single response. Maybe nobody watched it
If you watch this video - at about 37 minutes he does a interesting test which shows the effect of cable directionality.
I can clearly hear an audible difference - watched on a phone I doubt the difference will be so clear - watch it off something half decent Asus Xonar ST Souncard into Senheisser headphones - HD558 I think they are were about £120 its easily audible.
A volume / pitch type change is audible - but its not that its about what he describes as it getting out of the speakers.
For the cables dont make a difference brigade something to chew over - if that small amount makes a difference you can only imagine what else does
Its a great Video to watch with loads of interesting info as well