Denons tend not to have specs that drop that low on ACD tests. Here''s a bench test from an older family member of the 4500, the 4200
https://www.soundandvision.com/content/denon-avr-x4200w-av-receiver-review-test-bench which yields more than double the number you mention.
The Onkyo 906 needing more volume probably had much more to do with the demands of the speakers than any indication of power. I can't find a bench test but 68wpc sounds low, have a link to a test?
Nad M25 power amp actually benched in an ACD test by S&V a very impressive
0.1% distortion at 194.3 watts
1% distortion at 230.7 watts
But comparing a dedicated power amp to an avr is somewhat meaningless, too.
ps ACD ratings only mean so much in the real world as simultaneous full demand of all channels isn't a real concern/need.