@decooney Much appreciate your thorough review of the entire course of discussion. I will try to clarify my position on each issue.
1) Why focus solely on the amp? Because mine is beyond its ten-year warranty period, long out of production, and frankly losing its grip on challenging material. So, what better time to reconsider tubes before committing to a costly new decade-long companion? Especially considering I changed speakers during that period.
2) Why ignore preamps? Because in my experience, it's the preamp that establishes the sonic signature, but you can't work on that until your output chain (amps/speakers) has become a constant in the equation. A prerequisite, if you will. I am ALWAYS looking at preamps and need no help on that question. Being stable at that position in the lineup at present, I must focus first on the amp, then the DAC, before playing with preamps, which for me is where the fun lies.
3) Why the balanced specification? Because this helps to limit an otherwise boundless field of choice. (Same with my requisite of silver, or at least non-black, finish). In my setup, balanced operation helped with impedance matching, gain, and long-ish cable runs. Not to mention manufacturer recommendations. So I became a "balanced guy," and if that seems arbitrary in one sense, it is surely not irrational in any sense.
4) Why the default position of tube pre + SS amp? Because I can't live without a tube pre (though I also have a fully balanced SS on hand), while my Legacy speakers quite likely can't live with a tube amp, as I have just learned.* Frankly, I am also lazy. Even if the tube amp is self-biasing, amps sit down in a dark corner of a dark room near the floor. Some use three different tube types, requiring matching spares of each on hand. I'm just not the born gearhead obsessive that so many in here are. (No knock on them -- I learn a great deal from the experts, the wizards, just reading their hugely informative posts in here).
Hope this clarifies where I am coming from.
*From two different Legacy dealers, one in LA and another in Minneapolis, both of whom also sell plenty of tube gear. ("High current, and running deep in Class A to emulate tube sound").