Not so high end:

Six Budget USB DACS Put To The Test! Clive Meakins checks out some USB equipped DACs and how to get the best out of them. USB DAC shootout featuring JPLAY and the Rega DAC, Beresford TC-7520 (modified + Burson Buffer), Halide Design DAC HD, JKDAC , M

There is so much happening so fast in this arena. Just google DAC TESTING and you'll see.