I got into a discussion with an amp manufacturer (solid state) the other day and he said his amp sounds better when using the RCA inputs rather than the XLR inputs. He makes his amps with both inputs, but prefers the RCA's.
I always though that using balanced connections was the way to go if so equipped.
His amps are probably single ended topology. A balanced (differential) signal requires conversion to single ended signal before the single ended amp can use it. Balanced to Single Ended converters (BAL/SE) come in different types, and levels of performance. Usually it is an opamp. The additional opamp(s) can change the sound a little, or in some cases a lot. The ones that change it very little, like THAT 1200, are relatively expensive so not used in consumer audio. High open loop gain opamps need lots of feedback to work as buffers and that changes how they sound. rarely are opamps used with the gain structure that makes them sound their best, and each opamp has different gain sweet spot. A common sight is the TI LME 49xxx series used in unity gain. Nothing kills the music better than that, but it's everywhere. Thank you John Atkinson for spewing your editorial load about the LM4562, predecessor to LME49xxx series, as the risen Christ savior of audio technology back about 8 years ago. A whole editorial column about an opamp! omg A 'New Deal' for Audiophiles. not
An input transformer type of BAL/SE converter is mostly transparent, but they cost a lot (LOT) more so they are rarely seen in consumer gear. I think Purity Audio Design uses input transformers on their flagship preamp. YAY Go Bill!!
Balanced signal was created to reduce noise picked up in cables. It allows filtering out the noise picked up along the cable. Residential audio systems are not exposed to the kind of noise the pros face, so we really don't need balanced signals. Single ended signal can work just as well, if well engineered.
That said, my favorite amps always seem to be fully differential type though....
which I dutifully feed with differential signals when possible.