I hate the Harmon-Kardon target curve

I am assuming you mean the Harman curve that was derived by testing hundreds of headphones on hundreds of people including many experienced listeners -- and then documenting what most people preferred? Its not really a Harman specific curve but a record of what most people prefer that Harman measured......and that many other manufacturers have had success with now as well.

(Kardon in your title threw me off. So I want to make sure I understand what you are talking about.)

I got some of the first AKG headphones to utilize it and I love them. Sounds remarkably natural to me.

But each implementation is a little different.

Which headphones are you referring to? Here is a list of which ones hew most closely hew to the curve.