It's a Xiang Sheng dac -- but really, the USB dac piece of it is a C-Media usb dac.
Here is what System Info on the Mac says:
USB Audio:
Default Output Device: Yes
Default System Output Device: Yes
Manufacturer: C-Media INC.
Output Channels: 2
Current SampleRate: 48000
Transport: USB
I'm going to try using the mini-toslink output from the Mac, and then the toslink input on the DAC, instead of the USB input. But I don't have a mini toslink cable yet, so that test will have to wait.