I'm pretty content with my amp and DAC so there's only the headphone to upgrade
But, the TH600 is really growing on me. It is quite the refined headphone. Details and excellent bass impact. If I was smart I'd stop right here and pause to enjoy the music for the next couple of months, years, etc. with my current rig.
The TH600 has been good for jazz, electronica, reggae, folk, and blues. It's really an all around excellent headphone.