What dariusf posted are all very accurate. However, it also shows if bits are bits with no error or alteration, they also sound similar.
However, jitter is a complete different issue. There three primary cause of jitter, transmission, receiver and the media (cable). Jitter is caused by the turning on and off of the transitors in the circuit (in the case of circuit. In the cable, it's the charging and discharging of the cable. A more accurate term is dispersion. This also happens in optic due to the reflection when the light hits the fiber. That is why jitter is more difficult to control in TOSlink. If the fiber is glass based with a super thin diameter, the refection will be less and the jitter will be lower, but that will be very expensive (commonly used in telecom equipment).
Designer are faced with a tradeoff in clock recovery (at the receiver), a lower jitter generation will implied lower jitter tolerance (i.e. the digital stream is difficult to lock). So it came down to pscho-acoustic on how much jitter we can tolerate.
Modern design (because of IC technology progress) makes retiming a lot cheaper. Some DAC now have retiming built in (you can also buy a retiming device), so jitter becomes less of an issue in this type of device.
The overall jitter contribution of a cable is very little if the cable is short. Majority of the jitter is from the transmitter.
Jitter is too complex to explain in a single post. In relation to sound, any digital defect or improvement, is random (as opposed to analog IC). A poor cable will sound bad but it will not have any charcteristic of its own. Two good cable will sound exactly the same and there will not a warmer sound or bright sound.
So digital cable is more or less a 1 or 0. it will either sound good or it doesn't.
DAC are more interesting because different DAC have different error correction scheme. I burned a CDR with lots of error (not by intention) and it sounds vastly different on different machines. IMO, if you hear a difference, then you most likely have data error in one of the digital chain.