SQ difference XLR vs RCA ?

I can only speak for my experience. I have a Denafrips stack DAC, Pre-Amp, and amplifier that are all true balanced designs throughout.....I have Morrow Audio MA4 RCA and XLR cables.....same cables, different connections.

My Denafrips Thallo amplifier only accepts XLR inputs, so have only used XLR connections. I did compare the RCA and XLR cables from the Pontus II DAC to the Hades Pre-Amp, and the XLR connections were clearly superior from the very beginning, so much so that I didn't need more than half an hour or so before reverting back to the XLRs.

My assertion is that balanced designs should not be degraded by using an unbalanced RCA connection

I have gone from using RCA to XLR and back over the 40+ years of equipment/listening.  I've stayed with RCA for the last 15 of those years even with 5-meter runs of interconnects from my preamps to the amps.  While I definitely agree about CMMR with XLR, I believe if your system is clean and relatively noise-free, my experience is that RCA is a touch better.  If you have really good RCA or single-ended vs. balanced (XLR) equipment, the mfg has put all the money into single path amplification of the signal.  Even with extremely well spec'd balanced circuits, there are two active components each touching the + and - signals and in some cases even high precision component differences can result in slight sonic differences.  In my experience, the least number of active components "touching" the signal will yield the cleanest signal.  Now if you do choose balanced and XLR equipment, make sure your equipment is balanced through the unit input to output.  If it's a single-ended device with XLR inputs or outputs, you're only going to get a single-ended input signal and output signal.  No CMMR benefit !  

All my equipment is balanced (Audio Research Reference) and Audio Research recommends using balanced. I have tried both. I was unable to hear a substantial difference. Since, more and more manufacturers are headed that way (I think), I went ahead and switched over all my interconnects. More as a just in case thing.

If my system was not in what I consider it’s apex state, I would not have changed over. I would have applied the money to improving components. There may be other components more sensitive to the interconnect used. I am sure Audio Research put a lot of effort into converting the signal from balanced to unbalanced… this is audiophile stuff. They want every input and output to sound good, but extra conversion is never a good thing and tiny differences add up to making an impact. So, it depends on where you are in system building if you should worry too much about this.

All my equipment is balanced (Audio Research Reference) and Audio Research recommends using balanced. I have tried both. I was unable to hear a substantial difference. Since, more and more manufacturers are headed that way (I think), I went ahead and switched over all my interconnects. More as a just in case thing.

If my system was not in what I consider it’s apex state, I would not have changed over. I would have applied the money to improving components. There may be other components more sensitive to the interconnect used. I am sure Audio Research put a lot of effort into converting the signal …

Well put @ghdprentice - especially the “improving components” part.

If the context of the thread; we were smart we would make a list of the source and receiving component and whether it makes a difference.

• Gear with both RCA and Balanced maybe have different sounding paths
• Some gear may look balanced, but not be truely balanced.
• etc

On the equipment I've owned (Hegel, Cary Audio, and McIntosh), XLR wins every time. They all were fully balanced. The differences were most definitely subtle, but noticeable.