Perhaps I am too literal-minded. My first degree was in mechanical engineering, so if you want me to believe, you are going to have to produce Gray's Anatomy and show me which muscles (etc) do what.

For example, I know I can't breathe from my stomach, because it hasn't got lungs.

Equally I can't sing from my stomach because it has no vocal chords.

I have some idea of what "head voice" means (in one usage) because when I hum I can feel my sinusses vibrate, and I understand the theory of the Helmholtz resonator (and bass reflex and other resonant speaker cabinets).   

But a lot of it emotionally feels like mumbo jumbo designed to denigrate or deny the supplicant (like discussing the state of health of the Builder).