I just installed 1.5.5. I had been using 1.5.4 in demo mode and liked it, so paid my money and got a message that 1.5.5 was available. So installed it. Sound quality is excellent for me, but like some others, I am seeing some glitches that relate to the change from one song to the next. In one case, there was a multi-second pause between songs. Next two songs played properly in succession. Then, after a fourth, the music ended and there was silence. The Audirvana timer continued to increase as if something was playing, but no music. Meantime, in the iTunes window that indicated what song was playing, the selection changed approximately every 5 seconds. Finally, after about 10 minutes (the original song was 4:19), Audirvana stopped, and I was able to start another song.
I did not see this issue with version 1.5.4.
Running it in iTunes integrated mode on a Mac Pro, OS X 10.6.8. iTunes (11.0.4) is set to shuffle by songs. Audirvana prefs include no forced upsampling, and SysOptimizer set to extreme with all boxes checked.
