I have an ASUS Xonar Essence One as DAC/headphone amplifier for my iMac (Late 2013, Yosemite 10.10.3). The sound quality is fantastic, but the Xonar lacks a little bit of bass for rock/metal music. In iTunes i'm using the built-in EQ for optimization with perfect results. But what about apps and audio sources that don't have a built-in EQ, f.e. Spotify and Bandcamp? I have already tried Boom and Audio Hijack, but both produce sound distortion, as soon as i activate any EQ settings. I know, that there is software available from Asus, but it's only for Windows. Are there any other possibilities to get an EQ for all audio output under OSX?