Amplifiers will only accept an analog interconnect (RCA style or XLR). Some digital cables (coaxial) use an RCA connector and look just like a single channel of a regular stereo interconnect.
You want analog connectors. It is not as much a matter of the termination, as Bignerd mentioned, but of the resistance of the cable (if you are comparing coaxial digital to what you call "analog" RCA). Digital cables are usually designed around 75ohm resistance or less. I believe analog are typically around 100ohms. You could, in fact, use two digital coaxial cables if you were so inclined, since the terminations are identical and either one will work (you can also use an "analog" interconnect as a digital coaxial cable and it would work fine though may not perform optimally). What the difference in resistance actually means in terms of audio perforance...well, sorry, can't help you there...dunno as they'll both work in either application. Never gone through the trouble of actually comparing them. Someone with more smarts than me can splain that further, but the main differences are in the resistance, as I understand it.
Just taking your question at face value, you want analog I/Cs. Even when one is running I/Cs from a CDP or DAC to a preamp, you would want to use analog I/Cs.
A digital I/C is commonly defined as an I/C whose characteristic impedance, not resistance, is set at an industry standard: 75 Ohms for Single Ended/RCA S/PDIF or 110 Ohms for Balanced/XLR AES/EBU. A digital I/C is a single I/C used between a transport and DAC whose output and input respectively is supposed to be either an 75 or 110 Ohm impedance. The signal between a Transport and DAC is still in the digital domain. Hence, it's name: Digital I/C.
Analog I/Cs are just that; they are a left and right channel stereo pair that carries an analog signal that starts at the output of the CDP or DAC and runs throughout the rest of the system. For many reasons, there is no industry standard as to what analog I/C's characteristic impedance is. It's fairly all over the place from maybe 50 to 200 Ohms. Any I/Cs that are used between a CDP or DAC to a preamp, or from a preamp to amp that a manufacturer says are digital is probably saying they are "Digital Ready" which is simply marketing hype....like loudspeakers some years ago when CD playback was offering "Perfect Sound Forever" and a ton of speakers were marketed as "Digital Ready".
Finally, a bit of clarification. Impedance and resistance are not synonymous. Resistance is a DC characteristic while Impedance is an AC characteristic. Kind of a simple clarification but if that distinction isn't understood, all kinds of confusion can and usually does result.
Thanks for that clarification Robert! When it comes to electrical info, my synapses are not firing on all cylinders...or, er,...my elevator doesn't quite get to the top floor...you get what I mean!
So, out of curiosity, when you do mis-match the impedance in those specific applications, what are the likely results?
Despends on how the impedances are mismatched. Predominately, the cable's contribution will be dull or bright or, noisy or blunted transients. Whether the mismatch is on either side of the required impedance, efficient energy transmission is wasted.
When the impedances are correct, everything simply snaps into place.
Thanks for your explanation of impedance in digital interconnects.
I want to be clear about what causes a mis-match of impedance with respect to digital interconnects. The mis-match of impedance most often talked about in audio involves the output impedance and input impedance of two components connnected to each other. I gather that is not true for impedance mis-match in digital cables, because you said the proper impedance is established by the type of termination on the interconnect. That means the proper impedance does not depend on the output impedance of the transport/CD player or the input impedance of the DAC. From what you said, the only way an impedance mis-match could result would be the design of the interconnect itself. Is that right? For example, a cable that yields an impedance of 86 ohms instead of 75 or 110 ohms.
The most efficient data transmission can result when all three components are the same...i.e. output impedance of a transport, characteristic impedance of the I/C and input impedance of a DAC. Otherwise, signal reflections will result to one degree or another. This is not good. Rarely happens but if there's a mismatch somewhere between the three and if it's severe enough, the DAC won't even "lock" onto the signal.
The above is certainly not exhaustive on the subject but it's good info nonetheless.