Just got some info from Arthur at Matrix USA. Apparently there was a potential issue with driver compatibility when using the latest versions of JRiver or Foobar. Matrix did a lot of testing and at one point thought they needed to redo their driver. It had to do with DSD playback only, while PCM remained fine.
Turns out the errors were related to individual hardware (the PC, not the X-Sabre) being used, and the driver is fine. Girls Generation apparently has some insight into this. But my point here is this - if you experience DSD playback issues, contact Matrix and they will work hard to rectify it, whether it is your system or the drivers. They have good support and want to make their customers happy, period.