Best Headphone DAC/Pre-Amp?

These are VERY low impedance cans.I’m not sure of all in one units but for a 2pc.kit I HIGHLY recommend the SABRE DAC2 from HiFiMeDIY(Chinese under a Hundred $ delivered)like I have in my headphone system with either a Little Dot 1+$150.00...Schiit Audio Lyr II $450.00 or Woo Audio WA6$650.00...Stay away from the OTL All Tube amps,they are no good with low imp...Head-Fi.com is a fantastic place for all things headphone.

I am looking for an all in one unit. Hoping to find one that would support the very low impedance of the nighthawks and bring out the best performance.

What is your budget?Are you looking for the crystal clear SS sound or do you want a bit of tube glow?

Sennheiser Orpheus   is SICK!

@freediver 
 "What is your budget?Are you looking for the crystal clear SS sound or do you want a bit of tube glow?"

Thanks for the response! Looking for a crystal clear SS. No budget, looking for portable. Right now, I am looking at the Oppo HA-2.

I'm a HUGE fan of Oppo's DACS,truly world class IMO.At the price point of the HA-2 I don't think you can do better.Great choice.