Note: recordings are not standardized or any other way regulated to ensure an
accurate representation of the performance. If you want an
accurate reproduction of the original event, an accurate playback system is not going to achieve this without the source material being accurate, as well.
Let's consider the above: If one was to find recordings to have too much treble energy, especially noticable on vocals[an obvious bi-product of the close mike techniques], for example, would using a shelf filter to reduce treble on such vocal-based works be undesirable? Basicly, this is applying a correction target function to compensate for the original error[incurred during recording production]. I realize that it's not the theoretical job of the playback hardware to apply such corrections, but since the recordings are the problem, what else can one do, in order to get a more accurate representation of the original sound source from a realistic perspective?
Personally, I can not tolerate ruler-flat loudspeaker response on most recordings into the treble band, due to the above mentioned reasons. The excessive treble on most recordings removes the experience, that much more, from a natural presentation[unless one is accustomed to the tonal balance of a vocalist singing 24" in front of him/her], for me. I can, however, tolerate[and prefer] a rather flat[but not necessarily the flattest representation possible] total spectrum on headphones, as the in-your-head effect of headphones seems to go right along with that accentuated treble found on most recordings.
-Chris