Just to leave my input here. I have the Mac Mini, Audirvana, hiface 2, rega dac combo. Have been looking for improvements in the sq and thus decided to try the battery supply for the hiface 2, as the cost is negigible:
Just 14 £. Have just tried this evening and happy with what I am listening to. No blind tests, etc. so far but have listened to several songs I am used to and my impressions are more control and definition.
For its cost, certainly worth it.