And despite the modest power rating, this amp had startling dynamics.Because the ear uses higher ordered harmonics to sense sound pressure, and because this amp was really being pushed to hard to drive this speaker, higher ordered harmonics were showing up on the transients where the power is. IOW, it was distortion masquerading as 'dynamics'.
The mark of a good system is that it does not sound loud even when it is. This will be because distortion is controlled.
SETs make a particular type of distortion known mathematically as a Quadratic Non-linearity. This results in the primary distortion component being the 2nd harmonic followed closely by the 3rd. This gives you a rich sound, but again its due to distortion. The only class D amps that make that kind of distortion are zero feedback designs. You'll have to ask if they have a quadratic non-linearity; if they don't know what you're talking about don't buy the amp even if you don't know what that is either :)
Amps that make a 3rd harmonic might be interesting to you. The ear treats the 3rd the same as the 2nd, but amps that make the 3rd harmonic as the primary distortion component tend to be overall lower distortion. If you want the musicians to sound real this is a better way to go. Such an amp will still have some romance- it won't be dry.
Have you considered other tube amplifiers?