Balanced cables

Yes and no..Yes only if the signal path circuit is intentionally designed  by the engineer in an amp or preamp to be wired better to the XLR than the RCA connector. I read an article about ten years ago of an interview with James H. Cannon, the inventor of the XLR connector. Shortly after he added a lock on the three pin connector he passed away in 1950. I believe the interview was in 1949. He was asked in the interview if his XLR connector results in better sound than the RCA connector which was invented by RCA around 1942. He said "No..thats not the reason why I invented the connector". He explained it was only designed for better grounding with the ground pin to eliminate feedback when your running very long lengths beyond 20 feet to a hundred feet or more. He continued saying that if you have short lengths below 20 feet there is no feedback using an RCA to interfere with the signal and no difference in sound quality. Beware of snake oil.

elizabeth-that is partly true but only to the extent on how the high end component for in home use is designed. As I already stated a designer of amps and pre-amps can intentionally wire the signal path to an XLR to make it sound better than the RCA outputs, done for the purpose if one plans to do long cable runs in home beyond 25 feet. David Belles, who designs some of the finest solid state and tube pre-amplifiers in the world, does not use any XLR inputs or outputs on the back of his solid state or tube preamps, and they are quiet as a tomb. You will find single ended XLR inputs on the back of his top amps next to an RCA input only for the purpose of using the amp for very long cables in large environments. An XLR connector is just a connector, thats all. Its not a buffer or a processor and has nothing to whatsoever effecting the music signal. Its only function is to ground noise
feedback in a cable. It reminds me of the snake oil of many speaker companies selling models with three sets of binding post on their full range models. Even Spendor, my favorite British speaker company laughs at that nonsense as well, all their models, including their top flagship model, the D-9 uses only single pairs of binding posts.

Is this the same Stingreen who knows all about VPI gear, turntable set-up, and Quicksilver gear, the same Stingreen who years ago gave me specific advice as to how to upgrade the coupling caps on my ARC VS110? :-)
I was a bit surprised to see that you have expressed your disdain for Cardas cables. My opinion/experience is that as the quality of the electronics goes up and assuming that the design is truly balanced, than yes, there are marked differences among XLR cables. I totally understand the viewpoint of cable-skeptics because the differences are on one hand subtle and yet on the other, they can be huge. One analogy is a photograph that is ever so slightly out of focus vs. the same photo that is. As the quality of the gear increases, the perception of that perfectly in-focus image is better appreciated. I now own an ARC Ref 6 and ARC Ref 150se and I tried a variety of XLR's between the pre and amp and also various speaker cables and with each, I heard vast differences. The Ref 150se doesn't even have single ended inputs. ARC stresses in their manual that the quality of the XLR going into the Ref 150se is critical and they were telling the truth. I ended up with Cardas Clear Beyond XLR and Cardas Clear speaker cables and could not be happier. 
When I first upgraded my electronics, I read all I could about the opposing views on XLR's and saw the posts of those who say that with balanced cables, the differences of various brands are minimal and suggesting that Mogami Gold is all one needs because that is what is used in recording studios. This is one of those things that sounds good on paper but does not fly in reality. I started out with those Mogami Golds and they were the sonic equivalent of that girl that your mom says has a "very nice personality". A $600 pair of Morrow MA-6's were better, but the sound was etched, tone and timbre sounded "off", and my music was coming out of two boxes. A pair of top level Harmonic Tech's on loan from a dealer were very nice but not quite what I wanted. With the Cardas, tone and timbre are spot-on, I get the chills on the back of the neck that I never came close to getting with any of the other wire, my speakers disappear in my room, and everything is in focus. 

Fsonicsmith, as a point of information ARC line stages and preamps do not meet the criteria Atmasphere cited in his post that I referenced that would minimize or eliminate sensitivity to differences between balanced cables.  Certainly, at least, with respect to his criterion no. 4:

Atmasphere 3-22-2013
...  4) the output of the preamp should be capable of driving a low impedance load (2000 ohms or less) without loss of voltage, without increase in distortion and without loss of bass (this is the other big area where high end audio preamps have a problem, and also results in cable sensitivity).

ARC's recommended load for nearly all of their line stages and preamps is a minimum of 20K, and in some cases a minimum of 60K is indicated as being optimal.

So when "ARC stresses in their manual that the quality of the XLR going into the Ref 150se is critical," as you indicated, they are indeed "telling the truth."

Regards,
-- Al