I know I am resurrecting an old thread, but I do not know where else to place this post. I recommend both Fidelia and Audirvana Plus. I find Audirvana+ to sound a little better than Fidelia. I think it is because of its "integer mode" that bypasses OS X internal drivers.
By the way, I found an interesting limitation of Audirvana+. Normally it buffers the entire track before playing it. When I used an Audio Unit plugin, the buffering only just managed to stay ahead of where the player was in the song. When I used two AU plugins at the same time, there would be frequent dropouts. Next, when I played 24/96K audio files, there was stuttering for every little bit that it played.
What this means is if there is any problem with Audirvana playing a track, and you are using plugins, then look closely at them as the source of the problem. I do not have this problem with Fidelia.