Cultural detail: A singing style

In some tonal languages, tone carries more information than vowel quality does. To understand what this means, say we have five vowels (/a e i o u/) and three tones (let us mark them a, á, â, for convenience). If we were to take a sentence such as

ka lé pê mindâ lâktú patínmerông

and we conflated all tones and obtained either of

ka le pe minda laktu patinmerong
ká lé pé ...
kâ lê pê ...

or alternatively conflated the vowel qualities but kept the tone:

ka lá pâ mandâ lâktá patánmarâng
ki lí pî ...
...

Of these two alternatives, in those languages the latter would be easier to understand for speakers of the language. This is part of how drum language and whistled language works - although some extra redundancy often is added to ensure that there is sufficiently little ambiguity.

In many cultures with tonal language, musical tone is permitted to supplant linguistic tone in musical settings, sometimes making lyrics difficult to understand. I would assume a good composer-poet in those cultures would manage to make the musical and  linguistic tone line up throughout - or often enough that misunderstanding is unlikely or potentially even a productive thing (puns and such).

However, what if a style of music or musical poetry went the other way around, and instead of having melodicy tone trump linguistic tone, it had timbral melodies trumping linguistic timbre (= vowel quality), while the linguistic tone remains untouched? Essentially, a timbral melody, as far as song goes, would be something like
a e a i o
a e a i o
o a o e
a e a i o

so instead of, say

ka le pe minda~
ka le pe laktu~
patinmerong~
ka le pe minda~

 Where each syllable's tone is determined by the melody, you'd have

ka lé pâ mindô
ka lé pâ lîktó
potánmorêng
ka lé pâ mindô

where each syllable's vowel is determined by the vowel-sequence.

Timbre would be an important thing in the music of such a culture so instruments with adjustable resonance boxes or other mechanisms of adjusting the timbre would maybe be common. The most obvious adjustable resonance box is the mouth of course, so various things like this, this as well as jew's harps and such. If the vowel system is sufficiently small - five or seven vowels, maybe a simple musical scale of five tones and seven timbres would be doable as a xylophone or metallophone with rows corresponding to timbre and columns corresponding to tones. The full cartesian product of tones x vowels might not be necessary.