A: Preamp gain control is digital amplification mechanism. To adjust analogue gain of your device (loudness of speakers) you shall use device volume buttons, or Neutron’s Master HW gain. Digital gain in normal circumstances shall not be increased above the middle position of slider (>0 dB). Normal circumstances mean -  audio is normalized (usually all commercial music is normalized in studio). Using digital gain above the slider's middle position (>0 dB) makes sense only if your audio is not normalized and is quieter than usual, for example if you are listening to some custom recording. Amplifying normalized audio signal by using digital gain will lead to its guaranteed distortion in digital domain. Use digital Preamp to decrease audio gain only if you increase gain of some frequencies by equalizer. Use it with care and when you know what are you doing! Otherwise simply use standard hardware volume controls and do not care about it.