It depends on your room size and the listening material - movies, music, classics or the rock.
I have a pretty large room - 28'x16'x9' and I keep the volume on EP500 at about 7 o'clock (receiver level at zero) and the trim on 'Flat'. Otherwise it does sound (and measure) too loud, especially for listening to music. For movies it' OK.
If you have a sound pressure level meter, run the test tones from the receiver and check. But don't rely on the meter too much. For instance, the meter's readings depend on which measuring curve you are using - A or C. The C curve, usually recommended, imitates the human ear for loud sounds. The A curve mimics the human hearing at low volume. The readings at A and C setting are vastly different - what shows as 80dB on C curve can be 65 dB on A curve. It corresponds to the fact that your ears are more sensitive to the bass at high volume.
So, the result is that your ears are a pretty accurate meter as well, trust them. The sub should sound level should be approximately the the same as the main channel, may be a bit louder, depends on your taste. Get it higher for movies and lower it for classical music. Does the human speech sound too chesty? Lower the sub volume a bit. Does it sound that the orchestra doesn't have enough bass support? Raise up the volume. There is no fixed settings.
Setting speakers to small on Denon 5700 sets all the crossover points at 80 kHz which should be acceptable.
I set my M60 at 70kHz and the central speaker VP150 at 100 kHz. To me these settings provide the smoothest transition from the speaker to the sub. I'm not sure your receiver allows for independent settings.
