Why the hell do you need to EQ the bass on a DT770, and more importantly... 12DB? thats freaking insane. A little music with your bass sir?
If you want a 'nice' boost of bass, set the Preamp to -5, 32hz to +5, 64hz to +5, 125hz to +2. This should make the sound more full on bass deficient phones. There is no need to EQ 250hz and above since most headphones don't roll off until well below that.