I built a kit from HiFiBerry with their DAC+ Pro, added the IdPi mSD card and 2 high capacity USB flash drives, and it's a truly awesome thing to behold (and listen to). It's connected to a Niles Audio SI-250 power amp which has "Music Sense" and level control, so it turns itself on and off, and I adjusted the levels to calibrate it to the JRiver volume control. The amp powers B&W CM-9 speakers.
It's pretty incredible. Very low power draw when not being used, and I can play anything, anytime using Panel on my Mac.
Thanks JRiver!