Well, this maybe a monkey wrench observation, but it is totally (if you know the genre and the vocal physicality of the person I'm going to cite) on point about timbre; and perhaps as it is totally out of our genre, it even means more.
I'm talking about the most incredibly talented a capella pop/jazz group I've ever encountered live, Pentatonix. And as we've now mentioned the timbre of two of Chanticleers incredible basses, I add to the timbre perfection of their bass, Avi Kaplan. It doesn't matter a hoot whether the medium is alterned by natural acoustics or by electronic means, a timbre is a timbre. And when it is paired with exquisite intonation, superb musicianship and heart, it still is as close to perfection in sound that we can recognize in this dimension.

Pentatonix rox.

I think of multiphonics as 'Musique concrète' --- you must accept what the instrument produces, not much choice of inflection. But interesting sounds. One of the highlights of my rather limited flute career was a performance of George Crumb's "Vox Balanae" (voice of the whale). The flutist must sing-hum and play the flute at the same time. I later played the same piece in concert as pianist: a very different experience. I wanted to play it as 'cellist, too, but never got anywhere near good enough at 'cello.