I set my Denon 3312 + P362 gain levels to + 4.0dB.
As others have pointed out, Denon likes to keep their voltage gain LOW, probably to improve specs like SNR, and crosstalk.
I also set my Denon 990 + Phil3 gain levels to +4.0.
If you look in the Parasound manual, it says to turn the Gain knob all the way clockwise to the
MAX gain level in order to
"reach fullest sonic potential".
As long as you are not hearing hiss sound from your speakers (dead silent), increasing the gain levels is just fine.
In fact, I set all the channel levels on all my speakers above 0.0dB.