They are very far apart in terms of signature and performance but I find them to be wonderful compliments to each other. When I want complete neutrality, world class detail retrieval and massive soundstage, I listen to the HD 800. When I want fun and musicality (and that bass) it's the TH-X00. Oddly though I've found both are not nearly as forgiving with bad recordings than the LCD-2. I still prefer the LCD-2 for all my Jazz albums. TH-X00 is awesome with rock and electronic.