Hello, first time user here and need some help with this question please, I have a Rotel A14 integrated amp that has a headphone circuit that is in parallel to the pre-output through a 330 ohm resistor. I need to know what this means and is this integrated jack on the amp good enough too drive my headphones. I have Sennheiser hd 599 @ 50 ohm, AKG-702 @ 62 ohm, and Hifiman Sundara @ 37 ohm. Or do I need a external headphone amp to drive all of these cans? Thanks for any help I can get from you guys.