I'm running Amarra 3.02 on MacBook Air, this works best for me > plug into DAC
Turn on Amarra >turn off iTunes (don't synch) >hit the i and make sure the output is to the DAC, hit rescan if needed, punch up the playlist and fold in AIFF/Flac albums directly into the playlist and go
Trial and error with iTunes and my audio taste. This is what I find works for me.
Amarra instructions are complicated and wordy, but the sound is excellent and full textured