Like many other topics in the world of high-end audio this one is controversial. Balanced lines have been around for a very long time now in the pro-sound world due to the extraordinarily long cable runs often necessary for studio, stage and performance. With cable runs sometimes in the hundredes of feet noise becomes a real issue. But most audiophiles are rarely using runs that exceed 20 feet. Jeff Rowland was one of the first in high-end audio to use true balanced circuits in his amps and preamps and does so to this day as he feels it to be superior. And his gear is certainly dead quiet, not to mention some of the finest sounding gear available. Balanced Audio Technology has also been very sucessful with their balanced amps and preamps. Be aware, however, that while some manufactures have balanced XLR lines in and out, these may not be true balanced circuits such as those used by Rowland and may offer no sonic advantage and may very well not sound as good as the single ended inputs and outputs on the same piece of gear.
Another very significant point, and herein lies the controversy, is the number of truly excellent and highly regarded amps and preamps that only come single ended. Names such as Convergent Audio Technologies (CAT), Jadis, Brown Electronic Labs (BEL), Audible Illusions, Joule Electra, and Blue Circle Audio, just to name a few, come to mind. I personally have owned many many components over the years and have had systems that were fully balanced (except my turntable), but most that were not. I also have been using 16 to 18 foot interconnects between my preamp and amp for over ten years, and to date the best systems I've put together have been single ended. In the end I believe you will find it is the component itself that makes the difference, not whether it is single ended or balanced. My advice is to choose the components you like the sound of using your ears rather than someone's sales hype. No matter what you say or do there will be those in the balanced camp and those in the single ended camp. Neither is right, neither is wrong, just different approaches to the same end. All of this stuff sounds good, the trick is finding out what your preferences are and working toward finding components that are a synergistic match with each other.