What is the best sounding DAC at $2000-$4000?

Getting the PWD MKII would offer the additional benefit of network streaming if you get the bridge - this will sound better than USB. I would get one used and give it a whirl.

I did a shootout of my original PWD against the Zodiac gold + Volitkus. It was close to a toss up but I would say the Zodiac probably won by a hair. However, I knew the MKII was in the works at the time, so I held out for the upgrade. The MKII took the PWD to a new level, and to my ears it is now materially better than the Zodiac. Throw in the benefits of the bridge option and the ample supply of very affordable used PWDs and the choise is clear (to me).