Mac mini won't recognize USB DAC after Yosemite update

I have been using a USB DAC (PS Audio DirectStream) with my late 2012 Mac Mini to stream audio via JRiver Media Center and the Tidal app. A few days ago I updated Yosemite to 10.10.4, and now the USB DAC has vanished from both Sound preferences and the Audio Midi utility. I was literally listening to music in JRiver as the update was downloading, and then after the reboot the DAC has just vanished and won't show anywhere. I've rebooted, powered off, etc both the Mac Mini and the DAC multiple times and the Mac just doesn't even recognize that it's there. I changed the USB port and cable, no change. Based on a tip I read elsewhere I also went to Apple menu -> About This Mac -> System Report -> Hardware -> USB to see if anything shows there, and there's still nothing. (Not sure what it would show as I've never looked at that before.)