Im no expert on your specific receiver,however I own a NAD T758 that I use to drive my center and rears only....
For giggles one day I plugged in some of my headphones into the jack just to see what would happen....
It "drove" some of my headphones,but not properly...heck it couldnt even come close to my $99.00 Magni Uber 2 in terms of volume,bass control,sound stage etc...
Unless your receiver is an exception to the rule(and no offense meant at all,I doubt at 400.00usd it is) typically modern receivers cannot drive anything well above the most simple to drive headphones,and the HD650 isnt an excessively easy headphone to drive.
Vintage(pre-1980) receivers are a totally different story,but of course they dont do 7.1/9.1 decoding and all the others bells and whistles that modern receivers have.
Back then all receivers did was play music,and they did it well.Today most modern receiver makers try to cram so much under one chassis that usually the headphone jack is nothing but an afterthought,otherwise the headphone amp market wouldnt be exploding as much as it is.