One point that has not been mentioned, but which you may want to consider, is SS amp design. Some designs produce brittle or hard highs, while others have a smoother roll-off and fatter midrange. In the case of McCormack's DNA-1 amp design, harmonic and subharmonic distortion mirror in many respects that found in tube amps. As observed by John Atkinson in Stereophile's review of the DNA-1:
Also, J.Peter Moncrieff in IAR-80 stated much the same about the McCormack's DNA-500 design:
I have a tubed pre and an upgraded DNA-1 Deluxe so that I can take advantage of the strengths of tubes and SS.
While the DNA-1 does have some upper partials present, these are not isolated but are accompanied by the lower partials in an almost regular descending series. This is typical of tube amplifier performance, tending to sound smooth and "fat" rather than grainy.
Also, J.Peter Moncrieff in IAR-80 stated much the same about the McCormack's DNA-500 design:
Some other solid state amps evince a diamond hard, clinically sterile sound, which calls attention to itself as seemingly clean and pure. But this hard, sterile sound can actually be a symptom of expansive odd order distortion, a common problem with some solid state circuits (in contrast, some other solid state circuits and most tube circuits tend to have compressive odd order distortion which sounds different, usually soft and grundgy). The DNA-500 sounds like clean real music, and you can't ask for more than that. There's no hint of the hard sterility that plagues many other solid state amps.
I have a tubed pre and an upgraded DNA-1 Deluxe so that I can take advantage of the strengths of tubes and SS.