First decide what headphone(s) you want to use. They have the biggest impact on the sound quality. Then pick an amp or amp/dac based on the impedance and power requirements of the headphones.
As far as DACs go the D2 has a really good volume control, better than the Benchmark I think. And the measurements are superb. However the Benchmark has some features that are nice. It's up to you whether they matter to you.
More important is whether the amp sections of these DACs will work with your headphones.
Warm lush organic = tubes maybe an NOS DAC. Be sure that's what you really want, I don't think you will get that from either the Benchmark or the D2. The D2 is very transparent, and Benchmark is a pro company so it is being sold to people who need the truth.
Personally I think it's a mistake to try to get a specific sound from a DAC. Electronics and cables should not alter the sound.
You will likely find that after a while you won't be satisfied by electronics that behave this way.
Pick your headphones on the basis of the type of sound you like. Then you can swap them depending on your mood.
Probably it's not economically effective to use a $2000 DAC with $200 headphones. In most cases the cost should be more or less equal to get optimum results.
good call re: "Personally I think it's a mistake to try to get a specific sound from a DAC." that's what the eq is for, right?
i actually tend to listen to 90% of my music through Dynaudio DBM50 monitors rather than headphones so I guess that's a key to the DAC i'm looking for. more monitor driver....
main contender right now is BMC PureDAC:
Grace M903 and Benchmark Media DAC2 HGC are the other front runners as well as....