Cables can distort the square wave form of the digital signal to produce jitter however a decent quality cable of reasonable length should not introduce anything that's audible; if it does, it's probably faulty. There's certainly no need to spend silly amounts of money on exotic cables.andyjm said:If you have studio experience, you will know that it is common practice to have a studio 'master clock' which is used to keep all digital devices in sync. This helps to avoid jitter being introduced by daisy chains of devices, each introducing a little more jitter as the clock goes along the chain.
In a domestic situation the clock is embedded into the datastream in the S/PDIF link. So it isn't just 1s on 0s going down the link, there is also a clock signal. While the data is robust, the clock signal is fragile and can be subject to phase errors caused by mismatched cable / termination effects. This in turn can introduce jitter which MAY effect DACs that are sensitive.
So while you are right that is is unlikely that a cable will be so poor as to cause data errors (wrong 1s and 0s) it is quite possible for a cable to cause clock issues.
As explained above, this is generally avoided in studios by using a master clock, distributed separately from the audio data.
Good quality DACS have ways of reducing jitter to inaudible levels.