preamp inverts polarity

Kalali,

It’s pretty simple. The bias level in a single ended amp defines how negative a signal it can pull it down. If the source drives it below that bias level, the gain device goes more non-linear and eventually shuts off completely. It’s the electrical equivalent of trying to pull a vacuum in air. Push-pull amps don’t do that unless they’re deliberately mis-balanced. Instead, they transition to class AB and one half of the push-pull does all the work. That's why SET amps have such devoted followers. The way a triode distorts as it runs out of bias is very organic and similar to how air behaves.

@kalali

Just to be clear here, Push-Pull amps can be class A and also all triode. The 'air is single-ended' thing is a bit sketchy and also a bit of a red herring, since air has nothing to do with how amplifiers operate.

The transmission characteristics of air certainly don't resemble electrically balanced operation. And no doubt there's more to the character of a triode than how it distorts in a SET. Its undeniable that many fans of SETs like them because they distort in a way somewhat similar to how air does. 

Even if what you say is true, which I actually doubt, it would not change the fact that at least 50% of CDs are mastered in reverse Polarity. SETs don’t magically counteract Polarity. There is no balm in Gilead. Not to mention the fact a lot of people don’t like the sound of SETs.

@geoffkait 
You make no sense. What you're saying here and up above makes no sense. What's more, you can't come close to proving it this or that was mastered in one polarity or another. The polarity of the fundamentals make no difference whatsoever. The problem of polarity lies in the the overtones and distortions generated by the instrument and the recording space. If you don't have those in proper phase/polarity, it completely changes the sound and it's pretty freaking obvious to even a sophomoric listener, much less an engineer who does this stuff for a living. If you're listening to stuff recorded and mastered by engineers that can't hear the difference between polarities and phases, you're listening to some real garbage. The polarity and phase of the spacial and distortion information goes a long way in defining the presence of the sound. Generally, positive polarity even order distortion gives the sound a crisp, clear, forward pop while negative phase distortion extends the depth of the sound field and presents more smoothly. That's the going theory on why odd order harmonics really stick out. They add a stiffness to the peaks of waveforms that sounds inorganic, because it is. 
I'm certainly no SET lover myself, but at least I know why people like them. And unlike you, I've sat around and listened carefully to positive and negative polarity distortion and I'm very aware of what it's characteristics sound like.