Why a "digital" coax cable?

Sorry for the noob question, just trying to learn...

What is the difference between a 75ohm digital coax cable and a regular ol' RCA/RCA interconnect?

For instance, would there be a noticeable difference (improvement) between a digital interconnect and an Audioquest King Cobra for connecting the digital out from my Squeezebox (or CD, DVD, etc) to the digital coax input on my integrated amp? If so, how come?

Thanks all!
I can tell you the physical differences between the two. A so called digital cable has a solid core copper wire such as that in a TV cable. It can handle alot of bandwidth. Most but not all interconnects are generally braided copper wire. Can they handle as much information as a coax, I don't know. I'll leave that to those who know.
While this doesn't really answer your question, I have discovered that there sre some cd's a friend of mine has made for me that won't play back if I use a digital cable. So I run a digital cable, and additional regular cables into another input to accomodate this problem. Anyone else notice this?
Sid, when you say "into another input", to what component are you referring?
A cable with the proper impedance will transmit a less distorted binary (ON/OFF) waveform, but, so long as the receiver can still distinguish ON from OFF there will be no problem.

Component video, which also uses RCA plugs, is another story. Even for a short (3 ft) run I found that a cheap version of video cables having the proper impedance produced a better picture on a TV set than some audio interconnects that I had on hand. But this is an analog signal, where distortion matters.
Each cable has its own impedance characteristics. Does your integrated have its own DAC? At the risk of suggesting the obvious: If not, use an analog cables between analog ins and outs. If yes, try the analog outs into the analog ins with analog cables, then try digital out to digital in with the digital cable. Use what sounds best.
The additional input would be the analog inputs on a processor I'm sure. What else could they be?
Yep, the integrated has both analog in's and also digital in's (coax and optical).

In a casual a/b I think I liked the digital connection better than analog (using audioquest viper analog interconnects, .5m, and a aq king cobra interconnect for the digital).

But it seems pretty clear that the king cobra isn't the "right" cable to use to connect the digital side.

I'll do more of a blind a/b later today once I can teach my wife how to switch between sources.

But I'm thinking a "real" digital cable might be even better, if the king cobra isn't meant for that use.

The source (squeezebox3) has built-in DACs that are supposed to be decent, but if I like the digital out better I guess that means I prefer the DACs on the integrated?
In response to "Drubin's) question, "Rwwear" answered the question correctly.
Appropriate cables may change your perspective, but, I doubt it. It will probably steer you further in your current direction. I whole heartedly suggest you investigate appropriate digital cables.