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..
Sennheiser HD600 or HD650 with a Bottlehead Crack amp. Total investment is probably about $600. The only caveat is you have to build the headphone amp but to me that just makes it more fun.
Read it's what audiogon is just for headphone listening. Many smaller companies offer the best stuff. Many of the reviewers compare tons of items. The relatively lower costs results in many who build a collection and can compare in ways that we often can't here with high $ speakers, etc. Cheers,
Take a look at the Topping TP32ex. You can find them on Amazon. It has a
good Dac, USB input, plus a digital coax and analog input as well. It is not
only a headphone amp, but is also a 50 watt per side digital power amp to
drive speakers if so desired. I have it and it sounds great.