Why is the "upd" (upgrade) or high-quality 1080p tag so vital for this specific movie?

It sounds like you're referring to a specific of Gaspar Noé's Irréversible (2002), labeled with terms like "Dual 1080p" , "Upd" (likely an update or upgraded version), and "Proper" (scene release jargon for a fix over a previous bad rip).

Whether your audio equipment supports ?

Furthermore, the UPD version of the film offers a level of color accuracy and depth that is unparalleled in standard definition. This is particularly noticeable in the film's use of muted colors and stark lighting, which creates a sense of unease and tension from the very beginning.

You can find the film on platforms like MUBI , which often features curated versions of Noé's work, or check specialized cinemas like the IFC Center for screenings of the new 35mm prints and Straight Cut versions.