They are really hard to compare without having the LCD-2 still here.
If your looking to recreate the sound of sitting behind the drums, the LCD-2 will get you closer to that sound. It has a more detailed texture of actually hitting a drumhead. Almost sounds like real life on a well recorded album, listen to Chesky Dynamic Drum Test, it's amazing on the LCD-2.
Really, I loved the sound of the LCD-2 but the weight and soundstage were not good at all to me. HE-400 has better soundstage, air, instrument separation, and I want to say speed also. Wish I still had them here to better compare.