Let me give you some backgound on my end. Right now I am running HD600's with a Crack+Speedball with an NFB12.1 as the DAC. It's a great sounding system - don't get me wrong - but it's not really my sound. I don't care for the bass on the HD600's. I find it uncontrolled, and bloated. I find the treble lacking in detail. The whole system is warm, but slow and almost muddled. I guess, it has the ....
I've auditioned most of the flagships - T1, HE-6 + HE-500's, HD800, TH-900's and I really feel in love with the HD800's. I'm on the journey (as many have been before) on the right amp + dac combo for me for the HD800's. I am looking for an end game setup.
Then if I was going end game... well I'm not sure... Schiit or Audio GD honestly
Either way always keep as clean a Dac as possible. The PCM based dacs... are not "un clean" but the lack the detail of the Ess Sabre and others