Although I have just used Rune for more than a week but I recognize that its volume level when playing music is quite low. It is low for both HDMI and headphones outs. This is true when I tested the case of OpenELEC to compare. I hope our Rune development team will take attention on this for the next release.
I ordered a DAC+ that I am waiting for the Hifiberry to deliver. Hope its volume level out is enough to feed for my amp Denon PMA-720AE rather I had to turn the volume knob much as the case shared above.