Why not compare cheap to expensive headphones? I'd much rather have the HD600 than any STAX. They just sound more correct to me.

Depending on what YouTubers you watch silver cables change the sound of headphones. So, not really a good source of information.

Equivalent in what? Place in the company product stack?

And cheaper how? You still need at least a 500 bucks (srm 252S) amp for them, whilst 99% of conventional design work with any 100€ or cheaper amp.