Apples to oranges comparissons, but you were asking in particular about the comparing headphones to the top end of speakers(wilsons, Genesis, Magnepan 20's,etc) and there really is no comparison. In all the measureable ways speakers win, freq range flatness etc. And true imaging and depth of field is something headphones will never pull off nearly as well as a properly set up pair of speakers with current recorded music technology. But, headphones are a very cheap and easy way to get something with very high resolution with little effort and money(compared to highend stereo setups).
Every once in awhile I am tempted to get something higher end than my HD650's and my small homemade tube amp, and then I listen to my computer speaker setup and realize that even the Orpheus setup's I've demoed don't come even close, let alone the full setup in the basement. For the record my computer setup is a full Infinity Modulus setup(Original system not the crap they have now. Emit tweeters, servo subwoofeer, etc). It's measured in room response is from 18-45k. So to each their own, but I personally can't see headphones replacing someones Wilson X-2's.