Here is what I determined by designing and building many digital cables, and making measurements on those and others:
1) the 75 ohm impedance of the cable is critical and should be uniform over it's length
2) Termination of the 75 ohm cable to RCA plugs is a non-starter. Must be terminated to a proper 75 ohm connector, and a good one, like RF or BNC.
3) Use of pure silver in the 75 ohm cable is preferred, much better tonality.
4) 100% shield is beneficial
5) Conductor gauge is critical. Should be 26 Gauge or smaller to avoid skin-effect
Here are a few measurements:
http://www.audiocircle.com/index.php?topic=154425.0
Steve N.
Empirical Audio