A further thought that occurs to me regarding digital cable break-in: Since S/PDIF and AES/EBU cables will be terminated in nominal impedances of 75 ohms and 110 ohms, respectively, while line-level analog interconnects will generally be terminated in tens of thousands of ohms, and the signal amplitudes involved in each of those cases are not greatly dissimilar, in normal use vastly more current will be flowing in a digital cable than in an analog line level interconnect.
Therefore whatever break-in effects may occur in a digital cable, if any, will tend to happen far more quickly in normal use than would be the case with analog interconnects.
Regards,
-- Al