When trying to replicate Stax headphone SQ on speakers, don't forget to pay attention to the amp and power circuits. I liked Duke's linking of perceived speed to upper frequency behavior. I've found improved transient attack to be the biggest benefit to having larger amps and better power cords/conditioners/multiple dedicated circuits. Add to that some treble clarity, and you also get air which is a trait I highly covet. I don't think I've heard horns match hard domes in that area, and definitely not electrostats. Larger speaker cabinets also move less and provide a better launch for the wavefront. YMMV and good luck!
Speed kills....
Which is why I love 'stats so much. For myself, dynamics and leading edge transients are essential. Are there any alternatives in terms of dynamic "boxey" type (verity?) speakers that I should listen to? My present speakers are hales t8's (hales has been out of business a long time ago) and they are about as far away from that ideal as you can get. I want to go in a different direction for my FINAL set of speakers.