I recently impulse bought the DT 770 Pro 80 ohms Because guitar center had them for $120 and the return policy there is very laidback. I do notice that they are a bit bright and harsh in the treble for me and they don't seem to be that much of an upgrade from my MDR-V6 phones. People compared these with the 598s or 600s. Should I try and AMP/Dac with these 770s or do the 600s have a more neutral sound in the first place?
HD600 is closer to neutral in the first place, you might also be in need of burning in the DT770 + a headphone amplifier to give it the boost that it needs. HD600, too, would need an amplifier, more so than DT770, such as the Matrix M-Stage. DT770 isn't quite as demanding, but will certainly sound best out of a desktop amplifier as well.