>>What I noticed with the Sophias in reference to the M60s is that they were a little sweeter, had a little more density to the midrange tone, and a little more sense of coherency or cut from the same cloth sound (at least from upper bass to treble); however, the latter seemed, upon further listening, to be a coloration imparted on all music and ultimately became a bit of a distraction.<<
All of this is consistent with what you should expect from competent SET v. push-pull -- even OTL. However, I cannot reconcile your statements. At least within the terms you chose to use, I don't know how "coherency" can be judged a coloration. It can take awhile to get used to, after years or decades of hearing push-pull crossover notch grunge, subtle as it is, as normal. But I'm guessing that whatever you heard as a coloration was something else about the Sophia. I don't regard the Sophia 845s as objective as the Audions, but they get closer than most competing 845 SET amps. The Sophia design is a more in-your-face presentation, and that's not just a function of acoustic energy. It's more aggressive.
>>There was also something going on in the upper midrange / lower treble that showed up on some tracks.<<
That something was likely the 845A tube's signature upper midrange glare, which the B tube mitigates, as does (to a lesser extent) the 845A Cryo. I know why amp makers ship with the 845A (it's dirt-cheap and consistent) but I don't know why any of them insist that's how their amp sounds best -- it doesn't. Not anyone's. I can't listen to the Sophia happily either with the stock tube. There is also some further tunability in the Sophias via the input, driver and rectifier tubes. It's not as simple a circuit as Audion's. The downside is less palpable intimacy and finesse. The upside is you have more tubes to roll for custom contouring!
>>The Atma M60s had significantly more drive, a larger soundstage, more air on top & weight on bottom, though none of the aforementioned was perceived as lacking while listening to the Sophias.<<
Ralph's M60 is a muscular amp and it has deep bass performance more precisely defined and textured than almost any SET amp. Can't comment on the soundstage differences since when I've heard both of those amps, soundstage was as large as I could want, appropriate to the music and the room. That none of these comparative shortcomings were perceived when listening to the Sophias shows vividly how subjective evaluation is. A/B comparison can make both contenders sound "wrong."
>>I have heard that the Sophias have a lower noise floor than the Audions?<<
They have in the past, though to me the difference was not actionable. Audion has recently changed their power transformer shielding and made some other internal wire routing changes, in part based on results from some work that Bob Hovland did on my Black Shadows. These amps are now as quiet as Sophia's, which were the quietest 845s on the the market, previously. You can also run the Audions very quietly by virtue of their high input sensitivity. If you have ample gain in your preamp, you can run the input level controls quite low and use more of the gain in a quiet preamp. In any case, this nosie floor difference between the two brands' 845 amps is now effectively moot.
>>Although noise didnt significantly factor into my evaluation of the Sophia, I wouldnt want it to be too much higher. Can this be a distraction with the Audions?<<
I'd need to know you much better to say. I've been listening to tubes my whole life, and vinyl too. What's a little power amp noise after all that? Power amps are quiet compared to recordings and sources. There's noise in the world, including at any live performance of music. Compared to my guitar amps, my hifi amps are silent. I didn't consider noise a problem with my Audion power amps before and they're over 10db quieter since Hovland had a go at them, so I never think about it. on the other hand, I know people who love the sound of a tube amp but because of scant spurious noise, they listen to solid state they enjoy less. People are funny.
Phil