Digital XLR vs Digital RCA

This is somewhat of a controversial subject.  I have read some people state that AES/EBU XLR digital interface has design issues and not as good as RCA/BNC.  Others say that AES/EBU is far superior.

You can run both cables to the DAC at the same time and just A/B the source input on the DAC.

How you gonna compensate for the 6db diff.?
Any level control you insert will affect the SQ.

The better cable with RCA connectors sounds much nicer.

I was told by someone who designs high-end DACs that a balanced digital cable is preferable to single ended and that if only RCA connections are available it’s still better to use a balanced cable with RCA adapters.  I have no technical understanding of why this would be but just thought I’d pass it on FWIW. 

It doesn't matter to my current Directsream dac XLR or RCA but it does matter to the source feeding the dac apparently with XLR being most popular. The Directsream likes the I2S input the most with my Perfectwave transport sounding best using the I2S  output from transport to I2S input in dac. Using an HDMI cable has much improved the sound. When I get my dedicated Auralic Aries G2.1 streamer I will use an XLR digital cable.