KrisBaliThat translates to the 6xx has a thicker, warmer and more smooth sound than the 770 with more body in the mid bass, it also is less fatiguing for listening periods and has better comfort once the headband is loose. The 770 is more comfortable out of the box. The sub bass on the 770 is absolutely excellent with a powerful kick and deep rumble with relatively quick decay (80ohm). Mids are a bit hit and miss but provide good clarity but are quite thin. Treble is quite sharp and can cause your eyes to squint when sibilance is present compared to the soft treble of the 6xx. Mids in the 6xx are absolutely fantastic, second only to the LCD2.
KrisBaliI own both (250 ohm version of the DT770). The 6xx's are better / more neutral. But I still like my 770's a lot. They have amazing, deep bass look cool, are built like a tank and super comfortable.