For what it's worth, I filter out 70Hz (-3db) and below (-12db @35hz) from the amps and speakers (using a pair of passive filters) and I am letting my ML Depth i subwoofer handle the bottom range; IMO, this has worked wonders in driving the Omega speakers with the Franks with substantially less distortion; I don't detect any distortion, but if there is, I have no objections to it :)
The point is that unless the amp is outright clipping, the ear does not detect the distortion as such- in almost all cases, the ear converts distortion into tonality. But because the ear also uses higher ordered harmonics as a loudness cue, if there are higher ordered harmonics in the signal, the ear will hear that as louder.
In an SET, the higher orders start to show up when the amp gets to about 20-25% of full power. Since music has most of the power in the transient leading edges, if the distortion is only showing up there it will come off as 'dynamic'. Lots of people like that (often though without understanding how its happening) but it certainly isn't natural!
If you really want to hear what an SET does right you need a speaker that is efficient enough that the 20-25% of full power is not exceeded.