Just wondering, how well will the O2 amp drive the HD 600's or similar headphones of that sensitivity and impedance? I know when I do upgrade, there will be better amps out there but I'm just wondering if it could nonetheless drive them to their full potential.
It will drive HD6x0 without a problem. Mine is pre-set to the lowest gain (1.0/2.5x), not the normal (2.5/6.5x). I just got K340 (400 ohms) in the mail yesterday. It's driving them fine on high gain--what would normally be low gain--between 10 and 1 o'clock on the volume dial. So I have no doubts about its ability to drive HD6x0. Technically, it should drive 600 ohms. Whether that particular combination sounds best is a minor debate amongst O2 owners and I haven't tried it yet.