which DAC to buy ?

If refinement is the first priority, which DAC would be your choice:

Dodson D-263
Kora Hermes (last version)
Audiomeca Enkianthus
Audio Aero Prima
Personaly I think either the DCS Delius or Elgar surpass any of those you have listed.
I have an Hermes 24/192 and an Electrocompaniet ECM I use as a DAC. Hard to beat.
I just auditioned the audiomeca in my home last week and bought it. I has a top Dodson. I hear less harsh edges, a more quiet background. I also added a CD transformer. It made soundstage bigger and made instruments seem more destinct with both dacs. I really suggest you listen to one if you've got some extra cash.
I just purchased a Kora...it is fantastic.The one you did not mention which is also great is the bel canto!
Add the audiologic 2400 to your short list...with the right NOS tubes it can compete with the best.