Hmmmm, I equate 'laid back' with 'relaxed', 'easy', 'non-fatiguing'... so to have a meaningful conversation the difference in meaning attached to the phrase would have to be overcome first.
To me, 'laid back' has nothing to do with a lack of highs or speed. It has to do with a lack of artificially-generated loudness cues that the human ear perceives as brightness. How you would differentiate this from a tilted up tonal anomaly is that 'laid back' measures flat on the bench and the tonal anomaly does not.
Thus, 'laid back' is a lack of coloration of the odd-ordered harmonic type (you could listen to a laid back system, get the full range of frequencies, and not be oppressed by the volume, with no sense of having to turn it down). I often perceive transistor amplifiers as not being very 'laid back'; not very relaxed.
So- if this is not an acceptable meaning for this phrase, then we need to sort out what this thread is about, right?