BD DT 990 come with 32, 250 or 600 ohms? Which did you picked and how they worked? Suggested for FiiO M3K is 16-100 ohms. 32 should work out of box, for 250/600 I would assume amp is needed? I am asking because I have FiiO M3K myself, soon, and I am looking closed headphones for it, probably end up 32 ohm BT DT 770 or AKG 550 mk3.