Combining staff positions (additional range?)

Let's say I am a tuba player and I want to play my low Bb (Bb1), or a flute
player and I want to play a D6.

These notes are considered part of the core range of the instruments and
are not written as 8va or 8vb.

It appears to me that there is no way to express these pitches with
SMuFL/Bravura Text in a text editor, is that correct? I tried to combine
multiple staff position characters together with no success: *Combining
staff positions (U+EB90–U+EB9F)*

Forgive me, as a new member of the community, is using a font like Bravura
Text in a web page (not a music notation program) a goal of the technology?
I love the potential of it: creating small components to natively display
notation on a website. But perhaps I am alone in my endeavors as the
primary goal is focused solely around notation programs. I'd love to learn
more!