Actually, one of the central tenets of proper blind comparison in the field of audio is to level-match upstream variables (e.g. DACs, amps) within 0.2dB (typically at 1KHz). This is a pretty discriminating standard.
The bulk of audiophile "experience" out there isn't properly level-matched. The resulting error from matching upstream electronics by ear will be audible by ear.
Edited by 3X0 - 6/24/14 at 7:51pm