A major acoustic requirement for a faithful reproduction of a music event is the 'fullness' of the sound and the sensation of being surrounded by the music you hear as you do at a concert hall, a church or a jazz club.
For classical music, look at any good concert hall (not mentioning a church or cathedral) and try to find major surfaces of absorption. You will probably have to stick to the observation that only the chairs and the spectators have such effect, and so they do to a modest degree.
The SMT acoustic treatments are about treating the early reflections through proper diffusion, not by 'killing' them (or absorbing as more commonly known) but by reflecting them intelligently so the fullness becomes part of the listening experience.
Much can be said about the far too extensive use of absorbers in the portfolio of most acoustic material providers: as they are cheap to make they allow for huge margins, they always call for an increase of their use as they never arrive at really treating the real acoustical issues as by masking one issue they uncover 2 others etc.
At a time when the art of psycho-acoustics was not yet developed and most good sounding concert halls did so because their designers were kind of lucky, the acoustical concepts like "dead end live end" found their way to the residential and studio market as absorption is so much easier to implement than a truly enveloping sound, both in small (living) spaces as in taller spaces.
With the start of the development of psycho-acoustics in the 1980's and having become fully mastered only in the first decade of this century, the insight has come as to why a room or a hall is experienced acoustically by the visitor the way it is and above all, how recreate that.
This is the main reason why you will see that concert halls that were designed and built in the 21st century are generally of much better acoustic quality than the ones built in previous centuries and also could be made more versatile in their use.
A good introductory document to the basis of contemporary acoustic science can be found in this document that was written by reknown Kahle Acoustics in preparation of the building of the Philharmonie of Paris which was widely acclaimed for having excellent acoustics as from its first concert performance (its construction was achieved in 2015).
The SMT acoustic treatments are a practical implementation of the psycho-acoustics science: how does the human ear and brain interpret the acoustic characteristics of a hall and why.
The treatments can be divided in two categories:
1. the wings which are aimed to treat the frequencies from the upper bass to the highest frequencies and
2. the (helmholtz) resonators which treat the frequencies in the mid- and lower bass
None of the treatments involves substantial absorption, thus not adding to the power demand of the music equipment which otherwise needs to compensate for the lost energy!
Major elements applied in the SMT wings are the following:
Frequency smoothing which leads to a more balanced listening experience reducing listener fatigue, more micro-dynamics and a better focus of voices and instruments;
Time domain extension which leads to a richer tonal density and a better reproduction of the acoustical space of the peformance.
These wings are recommended to be used at the first reflection points primarily but more of them yields an ever increased sensation of sound envelopment.