Dumb Head Phone Question

I am looking at a pair of Sennheiser HD 700 or B&W P7 headphones that are available through my company's rewards program.

They would be mated to an Oppo 105 and W4S ST1000 amp.

The dumb question is will I need to buy a head phone amplifier?

If the answer is yes, what technical details do I need to take into consideration?

Also, I would welcome any comments regarding the head phone choice.

Thanks!