Thank you Rushton, Tom, Pbul57, Tvad, and others for your comments and insights. I really appreciate listening to others describe the same equipment I've heard. Imo, the Atma-Sphere circuit - whether in the amps or preamps - is highly revealing of virtually any change made to it. I finally grasp what RK means when he talks about 'listening to the circuit'.
Having heard the amps and preamps with and without V-Caps, I find increased tonal depth across the frequency range with the V-Caps. 'Tonal depth' being characterized as the sheer amount of harmonic and overtone information accompanying the fundamental. What I have not heard from the V-Caps is an increase in warmth, or put differently, an increase in pleasing second-order harmonic distortion that lends a sense of 'fullness' to notes. Lack of fullness is not lean tonality.
Because I presently use the amps and preamp as my review references, I've been round and round debating with myself how best to characterize their sound in contrast with other gears. Crudely put, 'thin', imo, means lacking information - one is not hearing all the harmonics and overtones available to be heard within ones audible range because they have gone missing - all else being equal, lost in the circuit. At this juncture I don't believe the Atma-Spheres are lean or thin in tonality.
Hopefully I'll solve this with a better vocabulary some day, but for now the way I parse things is to say the Atmas have plenty of tonal depth, but do not display the same tonal weight as some other components I've heard. And I cash *that* out not as sweet/dry or rich/lean, but as warm/cool, where warm suggests pleasing distortions and cool suggests a more analytical sound verging on displeasing distortions (more odd order). The Atmas are not 'cool', but they're not warm and I presumptively think that may be what some folks intend when they say they're thin or lacking tonal texture. In effect, texture is distortion. The Atmas do not convey less tonal information, they distort less, but its less of what turns out for us humans to be a pleasing distortion, and its absence is noticeable if that's how you like your music. I struggle with this, and don't mean to say any other person's characterization is incorrect; I just need a way to put consistently into words the similarities and differences i hear between the Atmas and other gear that will make sense.
Tim