Why Single-Ended?

Home audio, especially 2 channel systems with analog being the primary source will rarely benefit from balanced connections. Adding balanced operation in this scenario will only add more circuitry with no real benefit and likely have deleterious effects.

The only place in my room where I didn't have significant interaction between the room nodes and where the equipment might be set up was about 15 feet from the loudspeakers (there just seemed to be less bass in that spot; a nice place to start if you don't want microphonics affecting the sound). So this has meant either a set of very long speaker cables (28' if I was to keep them out of sight), or moving the amps to a location right beside the speakers and running long interconnects.

The latter was not possible single-ended without audible high frequency rolloff and loss of detail. But when I went balanced, that changed significantly and by also running short speaker cables, I suddenly has more detail without brightness; a more relaxed presentation overall. There was no going back unless I placed the front end of the system between the speakers (where it just did not sound as good due to room interactions).

So the quote above is false in anyway I can make out. In the case of a phono cartridge which is balanced to begin with, its helpful to not be getting any artifact from the tone arm cable. The source is always the best place for things to not get messed up!

 Two for the signals and a third is the ground reference.

+1 on your post above Herman, but I spotted this bit in it and though I might point out that this is a frequent area of confusion: the ground is not a reference in a balanced system (or shouldn't be; if it is, the balanced system isn't being set up correctly). The **reference** is pin 2 is referenced to pin 3 and ground is ignored (used only for shielding). This may be one of the most misunderstood aspects of balanced line operation. 

Ralph, I get that the signals in balanced can float relative to ground. I'm not knowledgable about how you  configure your circuits but I'm thinking you do not float the signal from input to output so eventually the signals do get referenced to pin one. I see what you are saying though. Balanced will work without pin one attached 

+2 ??

I'm not knowledgable about how you  configure your circuits but I'm thinking you do not float the signal from input to output so eventually the signals do get referenced to pin one.

We try to avoid referencing signal to ground as much as possible in our preamps as it decreases the Common Mode Rejection Ratio. One area that is tricky though is the volume control. Since two of the five inputs of the preamp are single-ended only line connections (with RCA connectors), the volume control is built with 4 decks (one for each phase of each channel) and it has to have a ground reference to work right with the SE inputs. 

How much potential sonic performance would I lose by using my SE preamp into the unbalanced inputs of a fully differential amp? e.g., my UV-1 preamp into the SE input of an Atma-sphere amp, or using this preamp with a Pass Labs amp.

There’s an impedance difference between fully-balanced and SE inputs, but in what way would sonics be different using unbalanced in a fully-differential design?
Or is it recommended to use a fully-balanced preamp to gain high quality sound?

An addition to my post;
The unbalanced cable runs would be short, 1 to 1.5 meters.