RCA or XLR Between Digital Separates?

I doubt there will be an audible difference, but XLRs are always better than RCAs for everything. I can't think of an exception.

Agree with Irvrobinson. The "balanced" format is what is used exclusively in the pro/studio world-for good reasons mentioned here many times. The XLR is 110 ohms vs the RCA 75 ohm format so they are not directly interchangeable, you can easily mix and match.

I was under the same impression but read in recent reviews that spdif was superior. Does anyone have any experience?

Like 99.9999% of the questions, it all depends on the component and cable. Last month I demoed an expensive highly regarded DAC at home for a week and found AEB/ESU was much superior to RCA eventhough the RCA digital cable is 3X more expensive. The only way to know for sure is try both in your system.

really depends on the data stream that is being transported and the length of the cable. For CD's bit rate 16 bit / 44.1khz, and cable lengths under 6 feet, likely no difference.

At the data stream rate is increased to 24 /96 or 24 /192 then you're quicky running out of bandwidth, and have to move to an XLR Digital cable.

On the pro side, everything at 24/96 and up is all XLR, or twin XLR, in a double wire double speed config.