A few days ago I wrote that in multiple listening tests we've found that there's no sonic advantage to using the XLR AES/EBU inputs on a DAC rather than the coax RCA inputs.
That raised the hair on a lot of necks.
Sorry to be so blunt but, in most cases (but not all) it's accurate. Differences in cables make most of the small differences.
What is the technical difference between the coax and AES/EBU digital audio signals?
Coax is single ended data and AES/EBU is the exact same data in balanced form. In other words, to generate the AES/EBU output the same coax RCA S/PDIF signal is placed on one pin of the 3-pin XLR connector, and that same data is merely flipped in phase and added to the remaining pin of the connector.
Same signal, just sent in balanced form. AES/EBU is the pro standard for sending data. The data itself is identical.
Why this can be confusing is that when we're talking about analog audio, balanced is almost always better sounding. That is because in the analog world, the benefits of balanced audio are useful. Any common noise introduced in the cable, or any distortions from the output signal can be reduced (or eliminated) via the common mode rejection of the input signal.
That's great for analog audio but it doesn't buy you much with a digital S/PDIF stream.
The one advantage of AES/EBU I failed to mention is that on some DACs, including our own, we can get higher data rates into the DAC by using two AES/EBU cables if we have a source that produces those. This is rare and really not the point of this rant.
At the EOD, for most applications, the actual quality of transmission of data and the resulting audio output of the DAC are unchanged between the two inputs as long as cables are properly chosen.
Whew! Sorry to be so technical.