09-28-15: Jea48I suspect the main reason that may occur in many systems is that the supposedly symmetrically designed digital cable is not truly symmetrical at the very high RF frequencies which comprise the risetimes and falltimes of the digital signal.
You guys that are using a digital coax cable with a solid core center conductor that connects your CD transport to your DAC, you should be able to hear a difference in SQ when reversing the direction of the digital cable.
Try it!
Minor physical differences between the two ends of the cable in how the connectors and wires are mated and/or soldered together will result, at the tens of megaHertz and higher frequency components which are present in those signals, in differences in VSWR-related reflection effects. Which in turn will depend on the impedance characteristics of whichever of the two components each end of the cable is connected to. Which in turn will result in differences in waveform distortion, or lack thereof, on transitions between the higher voltage and lower voltage states of the signal as received by the DAC. In turn resulting in differences in jitter on the clock the DAC will extract from that signal.
Whether or not there will be audible consequences from all of that will depend on many system-dependent variables, including the exact output impedance of the transport within whatever +/- tolerance it is designed to, the exact input impedance of the DAC within its +/- tolerance, the jitter rejection capabilities of the DAC, the characteristics of the cable (including its length and its propagation velocity, which will affect the timing of how reflections and re-reflections from both ends of the cable are seen by the DAC), the susceptibility of both components to ground loop-related noise issues, etc.
Best regards,
-- Al