dedicated headphone amp is recommended regardless of headphone sensitivity or impedance. you can start as low as from little fiio and feel huge benefit.
A question about preamplifiers and headphones
I have a NAD C162 preamplifier (I also have NAD C272 power amplifier and a NAD CD/SACD M5 player). I wonder if I can purchase Sennheiser HD 598 headphones and plug them into the headphone plug on my preamplifier, or whether I might need to purchase a separate headphone amplifier in order to listen to these headphones. I have received contradictory advice about this matter. I would love not to have to purchase a dedicated headphone amplifier. I mainly listen to classical music in my own living room.