mbyrnes
500+ Head-Fier
HEX has more mid-bass and impact.
HEK has some of the best sub-bass in the game.
personally it comes down to preference. Listening to the HEK and HEX back to back, I strongly preferred the HEX. Soundstage, bass, overall tuning was spot on, perfect for me. The HEK seemed great for classical and jazz. Didn't like it at all for rock. The HEX with movies and gaming, with SBX, seems perfect. Nothing sounds false, everything just matches what my ears expect to hear.
So much at this price point is personal preference. Truly no right or wrong "best" headphone. Believe me, I wanted to love the HEK more, but for me it was too much.
I'm also finding I prefer easier to drive headphones, really high efficiency. They seem to play at loud volumes much better, which I've also found very true in the speaker world. It's always a compromise, but the HEX gets it right for me.