I might be the person referenced. I've only heard SET in two systems and both were the ML2.0. I remember being very impressed the first time. It was many years ago and I had already owned (and sold) Lamm electronics, but the amps were the hybrids and had a nasty bite in the treble that no tube rolling could cure. In hindsight I'm not sure how much of that was due to the speakers I had at the time. Anyway, the ML2.0 system I heard employed horn speakers (Avanteguard Duo) and of course the other system is Peter's. I've owned both Doshi and CAT amplification (obviously not SET) which I do like, but they have their drawbacks in terms of distortion, coloration etc.
However limited my experience I do think I understand the appeal of SET and how the choice of speakers is ultra important. Again, hard to know with limited experience but based on what I have heard of SET (along with lots of tube amplification in general) and compared to live acoustic music (which I hear often) I hear lots of coloration and a 'sameness' to the music. However in my opinion coloration is always there regardless of what the electronics are, it's just different colors. A lot of solid state sounds gray and tubes either golden or brown. If the presentation remains musical you get past it. I have just become incredibly sensitive to distortion - whether it's in the form of grain or a breakup in the sound and whether it's power, signal, electronics, speaker cabinet or room induced.
It's interesting you mention grain because I think it has been widely considered that good tubes are less grainy than SS, especially in the highs. Of course there are tube amps that are not well designed (using quite a bit of negative feedback for a tube product) that sound glassy or sharp in the highs (a friend of mine had a pair Octave RM220 monos that sounded like this).
There are actually not a lot of PP tube amps that I think are very good. They have tube flaws and flaws normally attributed to SS amps, which are mostly PP design.
Single ended hybrids or transistor designs are actually quite a bit more natural sounding and have less absolute distortion than many SETs...maybe that might float your boat.
For myself, I have gravitated towards SETs that also have pretty good measurements because, when you go with a simple, no feedback and seriously overbuilt transformers and power supplies, then under normal levels it is basically inaudible low order harmonic distortion.
BTW, Ralph is not really correct about the low order distortion. 2nd order harmonic has been demonstrated to be essentially inaudible, with pure tones, up to at least 3%. This is because the ear itself will make quite a lot of 2nd harmonic distortion but quite a bit less 3rd harmonic and less again of the following harmonics. With music it will be less audible. 3rd harmonic is already far more audible and can be heard below 1%.
The higher orders become increasingly more dissonant and more easily heard at lower and lower levels. What he is right about is that they do assist in masking of higher orders to some degree but it is not a blanket that stretches very far.
The distortion levels need to drop exponentially with increasing order. What is bad though from the pattern perspective is the absence of a dominant 2nd harmonic then 3rd 10-20dB lower in level followed by 4th at 10-20dB lower than 3rd and so on. This pattern follows the ears own self-generated harmonics and provides optimal masking.
Amplifiers that cut out the 2nd harmonic and the even order harmonics are disrupting this natural pattern and this then emphasizes the odd orders, which are less harmonically consonant or even downright unpleasant in the higher orders (5th and beyond). Without the masking of the lower orders and the pattern we expect to hear, the residual odd high orders will impact the sound quality in a highly negative way (gray and graininess, for example). Those colorations are IMO totally unnatural and are not heard in live music...warmth of real instruments is heard live and with SET and so this should be expected in a good recording. Do some overdo it? Yes, but not really good ones.
The golden or brown coloration in some tube amps often has to do with poor or undersized output transformers or inadequate power supplies and occasionally a poor driver stage. When those are properly addressed, there will be natural warmth but not strong coloration per se. Of course you are right that nothing is perfect.
I haven't heard the ML2 in a long time, so I cannot comment on the goldenness of its tonality but I don't think it makes everything sound the same.
You say you are sensitive to distortion but what about the distortions heard in SS amps? These are not consonant with music IMO, which is why extremely low levels of THD and IMD are not enough to purge them sonically.