"Dedicated" as in dedicated to headphones and not for driving speakers and a component of a regular audio set-up - a device created and sold specifically for headphones.
The concensus is that the headphone jacks on most amps like your Denon are an afterthought and do not provide the best sound quality. This is probably generally true but does not mean your Denon will not drive your K701s beautifully. I believe using the headphone jack on integrated amps or receivers is just more hit-and-miss. There are some brands, and even specific models, that have gotten some good reviews and Denon is one of those brands. Also, vintage amps seem to have generally been made with higher quality hp output than what is currently on the market but then you run into other issues, i.e. noisiness, reliability, etc.
I have had several dedicated hp amps and have found a vintage amp to outshine them all by a huge margin, but from what I have read, I probably got lucky and ran into some accidental but seriously amazing synergy. Mine is a Nikko from around 1980 and drives my Senns and K701s just beautifully. There are Nikko integrateds on Ebay on a regular basis and they are almost never very expensive.
