tube amps sounding like solid state and vv

Unsound, the funny thing about that is that transistors sound better on 16 ohms too. I agree with you of course :)

FWIW the underlying mechanism here is called negative loop feedback. It is a design device that is often used to reduce distortion. The problem is that in doing so, it is not perfect and actually *enhances* certain odd-ordered harmonics that the ear uses as loudness cues.

These artificial loudness cues are detected as 'hardness', 'harshness', 'brightness' and the like. Negative feedback can be used by both tube and transistor preamps. Those tube preamps that use it to excess will likely get a reputation for sounding 'solid state' whereas the careful transistor preamp designer can get his preamp to sound 'tube like' by limiting the use of feedback.

Component choice can affect things too, so its tricky to ascribe things entirely to one source. But in general you will find that feedback has a high collerlation with 'transistor sound'.

I think some designers try to get distortion and frequency response to the best that they can, at the expense of other probably more important parameters. Tubes often take a more reasonable stance- 1% THD seems high for a transistor amp but is common for a tube amp, which uses less feedback (and consequently might sound smoother). You get more a little more distortion but less of the types the ear objects to.

The bottom line is you still have to trust your ears. The benchmarks for testing won't tell you if the amp is really going to work.