Even though many experts believe the internal clock design should be more correct, there is a hypothesis that some people may actually like the type of jittery rendition brought by an external clock, not unlike some sort of distortion that can be pleasing to listen to (e.g. second order harmonic of SET). The fact that people can hear differences among clock cables may also imply that the cable does affect the clock jitter, which may be an evidence of external clock being more jittery in usual setups. The existence of 50 ohm vs 75 ohm clock input even among different products of the same manufacturer make things even more complicated.
The clock design is only one of the many aspects of technical implementation that affect SQ. Since SQ preference is subjective anyway, I guess one should just audition the different systems and ignore the implementation details (e.g. clock or Delta Sigma vs R2R, etc.) and factor in the costs of the clock and the clock cable.
)....anyway they did a very nice go through of one of the dCS DACs. They loved it but preferred the unit using only the internal clock. They actual felt the external clock degraded the sound.
