Perhaps it depends on the components in the system and their configuration as to whether the USB cable makes an audible difference or not.
Will a quality USB cable make a difference....
Will a higher quality USB cable make a difference when being used between a storage device (bus-powered mobile drive) and a music server (w/o DAC), as opposed to those used between a source (iMac) and USB converter/DAC? Can anyone confirm an audible improvement?