6. Why does the volume decrease when EQ is enabled?

A: The equalizer is implemented in the digital processing stage, and includes a filter stage and a digital gain stage.  Volume is controlled after digital-analog conversion.  The equalizer filter can effect a maximum increase of 6dB in a frequency band;  if this is done without lowering the digital gain, it could cause the digital signal to clip at 0dBFS and cause audible distortion.  Lowering the analog volume afterwards has no effect on the distortion.  Thus to preserve signal integrity, a digital gain of -6dB is added when equalizer settings are enabled to avoid clipping.  This does not affect audio quality except in so far as you need to turn up the volume afterwards.