Are you using any custom player like Audirvana or Amarra or Pure Music?
If you are using iTunes:
Look for Applications/Utilities/Audio MIDI Setup
It should look like the screenshot below, except you should have the VLink in the list. Click on the VLink icon
http://km.support.apple.com/library/APPLE/APPLECARE_ALLGEOS/TS3154/TS3154-soundtrack_pro-audio_midi_setup--en.png
On the right, you can set the output bitrate and sample rate. Set them to 2ch 16-bit integer and format at 44100Hz