@mitchb - I would contact PS Audio and ask them. PS Audio DACs are different from pure chip based DAC as they use FPGA (field-programmable gate array) with custom software to process the signal. There could be a problem there. Also, have you upgraded to the newest software version?
...From PS Audio's sales brochere:
DirectStream converts every input signal, both PCM and DSD, to single-bit, high sample rate 20X DSD signal. Use of a FPGA rather than an off the shelf DAC chip provides immense processing power, resulting in complete lack of digital glare, and allows the owner to download OS updates as they are released.