If I can't hear the sound of my own natural speaking voice when the
music is playing, I turn it down. I usually stay in the 90-95dB range
on peaks. Loud but not TOO loud.
This is probably wise. My measure of the quality of a system is that it does not sound loud at any volume. This can be done if equipment that makes higher ordered harmonics and distortion is avoided.
Denon's own specs are quite limited, too. They do provide this: 70W
into 8 Ohms from 20-20000Hz with .07% THD and 140W into 4 Ohms at
1000Hz with .7% THD. I see no specs for peak power. The 4 Ohm rating
at 1000 Hz just makes me wonder why they didn't spec it from 20-20000.
You can see from these specs how important it is to avoid a 4 ohm load! In high end audio, keeping the distortion down is important, because the ear interprets all forms of distortion as a tonality. Its particularly sensitive to higher ordered harmonics and intermodulations, which it perceives as harshness and brightness. This is why so many solid state amps sound harsh and bright- its not because of a frequency response error.
After you've had some time with the Denon, please post back here- I'd be interested in what you think of it.