The HRT HD has a great Stereophile review. Much better than the Halide, according to it. However, it says on their website that they are currently working on a driver to stream 24/192 files via USB in Windows. Don't most companies provide their own drivers to play hi def files (higher then 24/96) via USB in Windows platforms?
The Concero has a great review on 6Moons, and drivers are provided by the manufactures to play 24/192 (and ever higher resolution) files via USB in Windows.
The µDAC-HD DAC looks like another good contender.
Tough call! Have anyone listened these units side by side?