I think I get the gist of your question.
Some component preamps have headphone output jacks. They typically have mediocre sound at best. I know a dealer friend of mine had a Cary integrated with a headphone jack. He recommended it as a possibility for me for my headphone system. after a lot of research, I bought a Woo WA5… it completely and totally blew away the “included” headphone jacks on several high end integrated amps… and straight preamps. They are generally “add on” features and seldom compete with dedicated headphone amp outputs.
You just have to listen to a Woo WA5 headphone amp… then to alternatives… the difference in the systems I have heard have been absolutely incredible. You can see my systems under my UserID.