$5000 headphones is pseudoscience territory.

$30k for a speaker setup is reasonable for a professional recording/mixing/mastering studio, or slightly excessive for a hobbyist (but still more or less within reason).

$100k+ could "reasonably" happen if you're mastering for a complex Dolby Atmos system, but even then it's pretty excessive. And we're likely talking about mixing audio for movies rather than just music at that point.