Need Help buying headphones and head amps

My nephew is looking for quality headphones and a head amplifier for listening from his MAC computer. I know very little about headphones and head amps so I need some recommendations. After some research, I found the Sennheiser HD 650 Headphones and also the Grado GH1 headphones. The IFI - MICRO IDSD DAC also looks very interesting but I do no know. He will probably run a USB cable from the MAC to the head amp (any other suggestions?).

Does anyone have any suggestions for a high quality headphone and a head amplifier? Let’s assume a budget of $1,000 or less for both items. Any suggestions would be appreciated.

My plan is to give him 2-3 suggestions for each item and will then suggest he visit a dealer for listening and additional help. Where should he go in the downtown Chicago area for assistance? He needs a dealer that will help him make these decisions. Of course, purchasing items on line is also an option if someone suggests something. Thanks..
Running Senn 600 from Schiit Asgard 2 using Dragonfly2 USB DAC out of my Macbook Air.

Definitely well within the budget and sounds pretty good to me. I'd recommend upgrading the Senn 600 cable, however.

Cable Company, as Zd mentions, will lend headphones. Schiit has a 15 day return though there is a restocking fee. Music Direct has a great 60 day return policy...could get the Dragonfly there or at Audio Advisor (AA has a 30 day return).

You have received some good tips from earlier posters. Hope your nephew finds something he enjoys.
don't forget check out sony mdr7506,they are studio monitoring headphones,pretty cool sounding.Not so expensive ,but they give true sound.Using beyerdynamic a1 amp with them and grado ps1000.For quality sounds also important DAC in this chain
All, Thank you very much for the information above. It was very useful. I am reviewing Head Fi, Audio Consultants, The Cable Company, suggested headphones, DAC's, etc and hope to make some decisions shortly. Thanks again for all of the above suggestions. Audiogon is a great resource thanks to all of your posts.