Do people here actually known what a digital signal is? Basically it's a string of 1s and 0s and that's all represented by + and - voltages. Now as long as a cable doesn't convert 1s into 0s or vice versa, and it would have to be a pretty s**t cable to do that, the receiving device can recover the original signal completely. There is a piece of maths called "Shannon's Theorem" that proves this and that's been known for what must be over 50 years now.
This imperviousness to signal degredation is why CDs don't suffer (in general) from the type of pops and clicks you can get from vinyl and why DAB radio doesn't get the type of interference FM radio can get. The actual timing of the 1s and 0s doesn't matter either because the receiving device can store the incoming signal in a buffer and take it out at the correct rate. This is why CD players in cars don't suffer from the movement of the car.
So as long as a USB or any other digital cable delivers the 1s and 0s in a form where they can be recognised as such it doesn't actually matter what it does to the signal. After all you can download Gigabytes of computer information down a USB cable and it all gets to the other end in perfect condition and a digitised music signal is identical in nature.
So any talk of cables being able to modify the nature of a digital signal in some systematic way, for example enhancing the sound stage or providing deeper bass, is on a par with believing in the tooth fairy.
As I said before, some people will still hear differences between digital cables but what is going on is going on in their heads not in any objective world.
Chris