I personally used a Pan Am with a DIY ES Sabre DAC. Clean, spacious, neutral DAC with a tubey amp worked great for my TH600's.
General rule of thumb with these phones, they work better as an all-rounder with tubes which bring out the midrange and tame the highs, but much punchier and sparkly through solid state amplification.
Nice setup. You need to try the Chord Hugo one day. Sound very impressive with the th-600.