S/PDIF sounds more analog than AES/EBU

>>if both cables are in the system,they will affect one another-as they both will present a load to the transport and/or dac.<<

Totally untrue.

Each digital output has it's own drivers. Operating two at once doesn't degrade signal level or quality. You just don't want unused digital outputs active to reduce noise.

Furthermore, most components will only allow one digital output to be active at one time. In most cases, but not all, you must change the output setting to toggle between the two.

As far as I know the only difference in digital data transmission is jitter. Jitter manifests itself by creating side bands at very low level - very audible since not harmonically related to their root frequency. It can make impression of "lively" sound but I'm not certain how it changes imaging.

The reciever chip would be the same but the interface would be different from the input connector to the chip, and of course you are using different cables. Any or all of this could cause it to sound diferent. You may prefer the AES if you used a different cable. Isn't audio fun.

While making a comparison,it is easy to toggle between two cables to make a decision.But, if both cables are in the system,they will affect one another-as they both will present a load to the transport and/or dac.
Indepently evaluate each cable,one at a time.Your results may not change,as I prefer the S/pdiff myself.More from a dialectric position and sonics.

While it is okay to have both cables feeding the DAC, one should never have both cables feeding an amp while using the toggle switch on the amp to flip from one feed to the other.

This can be a disaster as most amps do not shut down one feed as they source to the other.

I've done some comparisons IMS with AES/EBU and S/PDIF (RCA) cables and find that S/PDIF generally provided a deeper soundstage with a smoother and more relaxed presentation. The AES/EBU were more dynamic and upfront with a wider stage. Preferences depended on the individual cable brands as well as the particular recording I was listening to. Mostly though, I've settled on using S/PDIF at present (though my Tara 'One' has a BNC on the source end).

Tpsonic:
Could you explain in more detail why having both types of cables connected at the same time would affect each other, since one is selecting and de-selecting the inputs. All my comparisons were done with both cables connected and toggling between inputs.

Chris - As far as I know AES/EBU is the same thing as S/PDIF. It is used in studio equipment while S/PDIF is for the rest of us. Electrical levels are slightly different and it is balanced but the protocol is the same. My Benchmark DAC1 receives both with the same chip. Here is quote from WIKIPEDIA:

"the low-level protocol for data transmission in AES/EBU and S/PDIF is largely identical, and the following discussion applies for S/PDIF as well unless otherwise noted." There is also fiber-optic version of the same protocol know better from its Toshiba name "Toslink"

I don't know what could be different in your system - maybe this difference in electrical levels. Are both Nirvana cables of similar quality?

You should audition each cable separately.If both are connected and you are flipping a switch,then one is contributing to the other-both are "in the circuit".

The transmission and receiver chips are different for AES/EBU and S/PDIF.

That is the reason for the same transport and d/a combination usually sounding a bit different with AES/EBU and S/PDIF.

You'll need to try both interations to determine which is best in your system.