I also have the E12. Even driving a pair of HE-500 planar magnetics, I still leave the gain switch in the 0 db position. At about 3/4 full rotation on the volume knob, it's plenty loud enough for me. Sliding the gain switch to the 6 db position unleashes the full capability of the E12. With my Grado SR-125i cans, it's more than my ears can take. I haven't detected any limiting or distortion in the 0 db position with the HiFiMAN phones.