The Heritage Headphone Amplifier is intended to work as a digital analog processor for USB audio, optical, and coaxial inputs. Beyond it’s primary use as a balanced headphone amplifier, it also works as a DAC for powered speakers, making it the ideal desktop companion. Toggle the output switch to “Line” and the amplifier will mute the headphone output and enable the line-out on the back of the amplifier. Flip the switch on the back of the unit from “Fixed” to “Variable” and you now have gain control through the volume knob on the front.