could you point me to some documentation that describes how a cable could impact the spdif transmission?You'll find this article to be of interest. It explains how cable LENGTH can be significant for spdif transmission, by affecting jitter:
http://www.positive-feedback.com/Issue14/spdif.htm
Of course the degree of significance of the effect he describes will be dependent on many variables, that will be different from system to system. Those include the jitter rejection capabilities of the dac, if any; the risetime and falltime of the transport output signal; the degree of impedance mismatch between cable, connector, transport output circuit, and dac input circuit; the exact logic threshold of the receiver device in the dac input circuit; the data rate that is being transmitted; the amount of electrical noise that is present, etc. etc.
For a given cable length, different cable types will affect the degree to which some of those variables come into play, particularly impedance matching and noise pickup, both of which will in turn affect jitter.
Regards,
-- Al