Aaaaand here we go again. I've had many years of experience on this subject, and here's what I can tell you. Are there published AES papers proving that high-end cables make a difference? No. Can you hook up a cable to a meter, and have it spit out a different number than another cable? Yes you can. Inductance, capacitance, and resistance figures will vary quite widely, and you can change them just by arranging the same wires in a different fashion. Do certain wire arrangements have an effect on resistance to outside noise? Yep. "Star-quad" for example is very good at noise rejection. Frequency response in a very broad sense (think DC-100KHz+) can vary between cables.
Cables tend to fail double blind tests. Guess what - so do amplifiers, cd players, etc. Just about any audio related product other than loudspeakers will fail double blind tests, and I suspect even speakers with similar designs and response figures will probably fail as well.
Why would Sennheiser or anyone else use an under performing cable? Why do Canon or Nikon include a crappy $200 kit lens with their $2,000 DSLRs? Aren't they crippling their own cameras? Kind of, yeah. If all you ever shoot with is the kit lens, you aren't really getting your money's worth. If they included $2,000 pro grade lenses in their kits, well that would double the price of the camera, wouldn't it?
Cables are like any other audio product. There are some great values out there, and there are some really poor values as well. $300 or $500 doesn't automatically get you to certain level of additional performance, regardless of brand or design. That's like saying, what if I spend $500 on "a headphone", will it sound way better than what I have? I don't know. What kind is it, who makes it?
S/Pdif cables are in my experience by far the easiest to understand. Use the best possible conductor (solid core silver, as pure as possible). Use an insulator with the lowest possible resistance, one that gets as close as possible to a vacuum with no insulator (foam teflon). Build it so that it so that impedance maintains 75 Ohms from tip to tip, which means 75 Ohm connectors. This can be done for about $100/m. Unless you have source equipment well into the 5 figure range, I wouldn't bother spending more than that on a digital cable.
With every other type of cable, there is no "right way" to do anything. The possibilities are near endless. Of the cables I've tried starting at the bottom in terms of price, Signal Cable's Silver Resolution gets a heck of a lot right for the money. Going up from there, I've found Audio-Magic's Excalibur series to be very impressive. The newest entry level Kimber Selects are very good. At the high-end, I like Kubala Sosna, Siltech, and Jorma the most. There's also a lot of stuff out there that's very expensive, and lousy (looking at you, Nordost).
USB cables are still a black art, and the best ones are made by very small companies. I don't think the big guys (Cardas, Kimber, Audioquest) really "get" them yet. This is why its so unfortunate that Locus Design is gone, theirs were pretty much universally regarded as the best USB cables on the market. Ridge Street Audio will now have to try and carry that torch.
Edited by DaveBSC - 10/22/11 at 12:26pm