Atticus is warmer and slightly bassier and smoother of the two, so it would be the Hd650 of the two Eikon is still bold, but a step down from the Atticus in terms of warmth and bass. It has a little more upper frequency presence. For that reason, Eikon would be the HD600 of the pair. I'm not saying they sound exactly like the Senns. I am saying that if I had to compare the pairs, that's how I would describe it.