Ok so there is no best setting on max vol on the amp+ renderer as you said it depends upon the input signal. Or in other words you can have the input signal amplified more to lower distortion with a weaker input signal. As the input signal increases (louder music in song) the amp+ will distort more and the renderer volume setting must be lowered until the distortion stops.
The question is what setting should the amp+ renderer be set at when not in use? I do not shutdown the rpi2 and keep it running all the time. I just disconnect the Airplay or DLNA client when I do not wish to hear sound from the renderer and leave the renderer vol control alone at say 88%.
Does this hurt the amp+ or speakers attached to it? Are there small outputs on the amp+ speaker terminals with the amp+ at 88% but with no I Input signal?
Can a rpi2+amp+Volumio renderer stay at X%>0 Volume for infinite amount of time or must one lower the volume to zero, or mute the amp+ in the Volumio web app or shutdown the rpi??