I see. Well, I still expect most answers will be knee-jerk "all non-headamps suck". I've never seen much focus or attention paid to the entire topic of headphone jacks in other non-headamp products, except to repeat the usual mantra about them being sub-par, which in most instances, I can see being a pretty reasonable assumption. After all, "good headphone jack" is going to be on the feature priority list at nuber 2113. The receiver has an awful lot of jobs to do, there's a ton of technology crammed in there that make up the bulk of the cost. Wheras a dedicated headamp is made for one purpose only-- your purpose. But that's not to condemn all receivers, as I've heard at least 2 exceptions to the rule (granted at very high price-points).
Still, you won't find reviews written about them, or anything like a general consensus that "most Denon receivers have good headphone jacks", or some other such wisdom. I think, for the most part, it's a crapshoot, although, I'm certain that it's safe to assume that, in general, the better the quality the receiver, the better the quality of its headphone jack.
Mark