They're 95% the same. Unless you have them side by side, I doubt people would hear the differences. As for sounding like hell, I don't mean that at all. Just stating that the treble on the 600ohms is clearer and more extended, which makes it more present for me. Considering that the treble is already very omnipotent, I like that the 32ohm isn't as 'clear' up there.
BTW, I've had two 600ohm DT990s, and they sounded identical. The DT990 Pro is the one that has its own balance, yet still having most of the Premium's sound, with a large quantity of bass added.
I owned the 770/600 and what I got was the opposite of what I was expecting. The bass was at 11, so much, I couldn't focus on anything else. It was too strong.