I agree you shouldn't go above zero. I've noticed on my Onk, right around -3dB, I start detecting distortion. That however is unbearable so it's not even a practical concern.
My gain setting depends on source and program material though. On BluRays recorded in HD MA via my PS3, I never have to go above -20dB (this is less than a half watt nominal). With Netflix from my TV via HDMI, I'm usually good at -15dB but I do sometimes have to go to -10dB. Spotify via Chrome Video is usually -15dB but some songs I have to run at -5dB. I am in a 4200 cu. ft. room and 13' away from the fronts, 14' from the centre and 10' from the sides.
How do you know your M22s are not compressing? Did you ever run them as loud as now at your old place?
What is the calibration level in your Denon for your fronts?
