Audio -- pro or commercial hifi -- is probably the least well defined technical industry of all, and it's probably getting worse. We have very few means of asserting technical competence in many forms of equipment, and many of the technical measurements we do have can be proven to be telling less than the full story.
To make it worse, very few reviews are based on independent technical measurements, and very few of those purchasing or using the equipment understand the technicalities involved anyway.
For example, many amplifiers are sold purely on the basis of their distortion figures. Low 2nd, 3rd and inter-mod distortion figures must be a good thing... but it is easy to demonstrate that there is much more too it than that. I have used amplifiers with stunningly low distortion figures that sound excellent (to my ears), but I have also used amps with distortion figures a hundred times worse that still sound every bit as clean. And I have reviewed amps with extremely low distortion figures that sounded terrible...
I guess what I'm trying to say is that although test measurements and spec sheets are important, we may not always be measuring every facet that is important to human hearing.
As far as the cables are concerned, the issue is very much more complicated than most here realise. Interference is not simple -- there are many different forms of interference, operating over many different frequency ranges. A cable rejects these different kinds of interference in different ways, using different properties. And optimising one particular aspect will often compromise the performance of others. This is easy to demonstrate with the Vovox cable, which has lower inter-core capacitance than most but worse core-screen capacitance, and poor common mode rejection, partly because of its low twist ratio. (In general terms, the twist ratio of the wires is important in rejecting relatively low frequencies -- mains hum to low RF), while the screen is important in rejecting higher frequencies (RF).
Of equal importance is the nature of the sending and receiving circuitry -- and that changes dramatically in different equipment. Balanced cables only operate with their intended performance if the impedance of the two wires is exactly the same -- and that is often not the case in electronically balanced equipment, especially the budget equipment.
This may well be one reason why my own experiences with the Vovox cables have been rather variable. Those using the cables with microphones may well be getting more consistent results because microphone outputs and inputs tend to be better designed from the point of view of impedance balancing than line inputs/outputs.
Another issue which affects this interfacing issue greatly, but which is rarely considered, is out-of-band noise produced by the source. Again, not really a problem with most microphones, but a real issue with outputs from D-As.
Modern D-As generally use delta-sigma or other heavy oversampling technologies, all of which produce immense mountains of ultrasonic noise as an inherent byproduct. Some integrated chips are considerably better at how they control this than others -- some popular Crystal chips, are amongst the worst for this, some AKM's are amongst the best... But the point is that this out-of-band noise, if allowed through to the input receiver circuitry, can cause intermodulation and headroom problems -- which may affect the sound. The audible effect could be perceived as a bad problem, or equally it could be perceived as having a beneficial tonal affect (although it wouldn't be accurate or transparent). Different results will be obtained depending on how the receiving circuitry is affected, and that depends on how it is designed and what components are beign used. Hence the inconsistency.
Whether the out-of-band noise gets to the receiver is affected partly by the nature of the cable, both in terms of the way it conveys signal (the bandwidth of the cable, if you like), and in terms of the way it rejects the out-of-band interference generated by the source device.
The other aspect is cost, and the Byre is absolutely right in this. Vovox cables are relatively expensive and not at all suitable in their current form for wiring a studio complex. So they tend to be used as a 'tonal modifier' in specific applications. That's fine for those with money to burn and I'm sure the Hifi fraternity enjoy playing with such things, but for serious studio applications it makes little sense -- practical, technical or financial.
But even having said all that, the issue remains an interesting one, and I am still trying to get to the bottom of just what it is in this cable that produces the apparently pleasing qualities it seems to posses.
Technical Editor, Sound On Sound