new help with headphone amp

I'm new to this stuff. A couple of weeks ago, I
bought some headphones Sennheiser HD650 so I can watch
movies at night. I'm running those headphones out of
my Onkyo 601 receiver. Do I need to spend money to
get a headphone amp? If so, is there any recommended
ones that are not too pricey? Thanks

it currently works, but I keep hearing how great those headphones will sound if I had a headphone amp.