I had both.
HD 800 for a month or so.
First impression (always crucial) : subpar but fast. Harsh highs, constrained mids, tight (but dry) bass.
Second impression : elegant presentation, but everything seems on the same plane, soundstage is reasonably wide, but relatively flat, no depth, no height.
Third impression : all in all, boring (think a polite dinner in a bourgeois family, quite educated, yawn… Nothing exciting.
First impression (always crucial) : luscious and generous, fast, but always smooth and delineated. Airy highs, mids perfectly balanced and organically linked to highs and bass (no hard steps between phases, like HD800, think speakers problems with awkward cuts between mid, tweeter and woofer), and large bass, multilayered.
Second impression : after two weeks. Quite organic, a bath of music with many subtle details, very good placement of instruments.
Third impression : a lots of discovery to come in the realm of sounds. Quite exciting.
Edited by quantx - 1/12/14 at 12:13pm