I have been listening the Teton and the 4-45 again tonight, doing more critical side-by-side comparisons. I want to offer a bit more insight into the differences between the two amps, at least as I heard them tonight through my HD800s.
I have been listening to Frank Ocean's Channel Orange and Tame Impala's Lonerism, both of which I have listened to many times before through headphones or speakers. Both are in the rock genre, with multiple instrumentalists. The vocals at times are multi-tracked and backup singers are brought into the mix on both albums. Channel Orange is very well recorded. Tame Impala is not a poor recording, but is not mastered nearly as well as Channel Orange.
The major noticeable difference is that the Teton offers more detail and resolution at all frequencies, but especially in the mid-range. On Channel Orange, Ocean's voice through the 4-45 sounds comparatively recessed, lacks a bit of texture, and the backup singing and other vocal tracks are less distinct. On the Teton, Ocean's voice, the additional vocal tracks, and the backup singing have textural detail that is comparatively MIA on the 4-45. The Teton creates this detail without sounding clinical and as a result feels more musically insightful than the 4-45. The same improved detail also applies to the treble and the bass of the Teton, so the Teton creates a greater sense of air and it images better than the 4-45, especially front to back. The Teton also has better bass than the 4-45. That was my initial impression and it is confirmed again tonight. Bass guitar and kick drums seem ever so slightly attenuated on the 4-45 compared to the Teton.
The Teton is a faster sounding amp than the 4-45. The Teton's dynamics are simply exceptional. When I listen to the 4-45, the contrasts between loud and soft passages are not quite as evident.
The 4-45 has a bigger soundstage. I like this aspect of the 4-45 in general, but at times the soundstage comes across a bit like a "wall of sound". Maybe I am not a "soundstage monster". I own expensive speakers, the Behold Tanara, that create a more realistic soundstage than any headphone I have ever heard.
The 4-45 is certainly not a boring amp, but it didn't attract the same rapt attention as the Teton did tonight. For most music, the Teton is just more musically immersive. Yes, someone dubbed the 4-45 the "God amp". If so, I am not sure what to call the Teton, which in the most important respects sounds better than the 4-45.