http://www.toneboosters.com/tb-morphit/

i just saw this and i only just bought sonarworks reference!! luckily it doesn't have my headphones...

just demoing this now, What I like is there is some Eq adjustment and I can get very close to my studio 
speakers , which I trust .

I think you will find this plugin worth your money. I picked it and it is great.

I grabbed it as well.  Wish it had my phones on the list.  Flipped through the phones list for ATH and there were a couple that seemed to improve the sound of my head phones.  

It has mine (AKG 550 and Sennheiser HD 598)! Still, waiting for a sale as it's no real necessity.
Edith: first get the trial, as its only limitation is: "The trial/evaluation plugins are fully functional, except for parameter communication between the plugin and the host, which is disabled. Consequently, hosts will not store the settings of the trial/evaluation plugins upon save." And yay, it's a separate download.

Yeah, I'm trying the demo...
I have ATH50s and it makes a big difference (in improve mode). I'm not sure how flat the change is, but it's brighter. I only use headphones when I have to. Like when recording vocals. I never mix with them.
I'm not sure I see a reason for me to buy this, but it's nice to see Toneboosters back!
The gui is his best so far.
 

There is an update to it Morphit 1.01.

Actually, version 1.02 is now out.

I compared this with Sonarworks using my ATH-50x headphones.  The visible curve in the two isn't exactly the same (though is very similar) but I couldn't really tell the difference between the two switching back and forth with some pink noise.  Does Toneboosters have sales?