Why Single-Ended?

You forgot that we are discussing Fully balanced topology and not design of particular amp in general.  Setting bias point, as you described, can be done to single ended amp and has nothing to do with issue that we're discussing.  Please tell me how Fully balanced amp topology reduces third harmonic better than single ended amp.

It doesn't. The 3rd harmonic (which is musical to the human ear) occurs at about the same level or slightly less (see below) than the 3rd shows up in a single-ended design (this is assuming open loop).

Because the 2nd is pretty well eliminated, the result is (due to the ear's masking principle) greater low level detail since there isn't a 2nd order to obscure it. That there is more low level detail in such amps is not a subtle thing- its quite easy to hear. Its nice when the measurements and the subjective experience agree.

When I was speaking of the bias point I was not referring to the output tubes, but the bias point at which the voltage amplifier is set. This is not an adjustment; its the value of resistor in the cathode circuit, which can affect the distortion and gain structure of the voltage amp. In the case of a differential amplifier, this resistor is in the CCS circuit and its value can be critical. In essence the value can have an outcome on the kind of distortion the voltage amplifier makes, particularly when it overloads. I prefer to set that value so that the stage is clipping in a symmetrical fashion. This makes for more of a 3rd harmonic rather than a 2nd, but also can have the effect of reducing the amount of the 3rd harmonic.

You cannot eliminate capacitance between wires.  Low output impedance helps to lower effect of it, but it so does with single ended design.  It will be difficult to get rid of shield to wire capacitance since many preamps have balanced output referenced to ground.

I hope you are not suggesting that single-ended cables can run as far as balanced... I'm going to refer you to Wikipedia on this one.
https://en.wikipedia.org/wiki/Balanced_line

I also refer you to AES file 48 which I've mentioned several times. The Rane site has a great little article that should help clear things up:
http://www.rane.com/note110.html

The final statement in the quote above points to the possibility that you did not read my opening post in this thread. I will therefore repeat myself in saying that many high end audio products don't support the balanced standard, such as the preamps to which you are referring in that last sentence.

When the balanced line standard is not supported the interconnect cables become audible and then audiophile tend to spend a lot of time and money trying to eliminate the audible artifacts that result (IMO/IME its simply easier to just support the balanced standard). This is the reason why this debate is still around (as Herman points out) years on after we introduced balanced line to high end audio.

To Ralph's point about the audibility of cables; I settled on DIY CAT 5 cables as interconnects and speaker cable years ago. They are neutral configured as single ended over any practical length in the home. I encourage anyone who is on the cable merry go round to do the same and focus on things that have more impact. If you are a million dollars into your system and want to play around with mega buck cables then have fun. If you have a budget like me then cables are the last thing to spend any money on. IMHO playing with the placement of your speakers will have much more impact than cables and it is free. On the other hand, you can go with Ralph's approach and eliminate cables from the equation

However, as a DIY guy that builds his own SE amps I have the luxury of tuning the sound to my preference with the active circuits and don't have to feed the coffers of ridiculously overpriced cable makers. It is inconceivable to me that someone would pay $20,000 + for speaker cables. That tells me 2 things; PT Barnum was right and I'm in the wrong business

Honestly you need to audition all kinds of amplifiers (I have). They work best with different speakers as well. I personally don't like SET amps at all (and I've owned 101db and now 91db speakers and tried at least a half dozen of them). I tend to prefer 3rd harmonic over 2nd I guess. But the people who are adamant that only one way is technically correct or sounds right are to be ignored. 

Ironically, the best I've ever heard Avantgarde was Trios w/ basshorns on BAT tubes years ago. The audience gave standing ovations - but darn those complicated balanced amps :)

Thank you Ralph for explanation about third harmonics. I understand that advantage of the fully balanced configuration is removal of second harmonic to better hear the third one (that you try to lower?). As for the balanced cable - yes it can run further because of superior noise rejection but still suffers from effects of the capacitance between wires. There is no way of getting rid of it. Capacitance to shield is different story. Reducing it would require usage of low capacitance signal transformers. Otherwise - even if you completely "float" signal ground in preamp and amp it will find return, by substantial capacitance of power transformer, to chassis (that you earth ground) hence to shield attached to it. Am I missing something?

Rane paper shows XLR cable (pattern1) with shield grounded at female end only, while common XLR cables, sold in stores, have shield grounded at both ends.

It would seem so.

In order to support the balanced line standard:

1) pin 1 is ground, pins 2 and 3 carry the signal
2) the signal occurs between pins 2 and 3.
3) Ground (shield) is ignored
4) the system is low impedance.

Again as I pointed out earlier, most high end audio systems don't do so well with 3) and 4) nor for that matter 2).

If they did though, the capacitance becomes a non-issue in lengths of 200 feet or so (which should be practical in most homes- at my place they are only 30 feet).

So, Again. If the equipment supports the balanced standard, you won't hear the effects of the cable. IOW if you can hear the effects of the cable, its likely that your gear does not support the standard.