Disclaimer: For purposes of integrity, the equipment used to critique for this post is as follows. 1) FiiO E7 USB DAC, 2) Sennheiser HD650 headphones, and 3) AIFF audio files stored on a 2TB external hard drive connected via FireWire.
Haven't done this for a while now, so I thought I'd catch y'all up on my gear. :)
About two or so months ago, I upgraded to iTunes 11 and, along with it, Amarra version 2.4 . Their claim on the Amarra website was that the player was fully optimized for the current iTunes, which had seen some revamping since version 10. To my surprise, both services used together sounded absolutely incredible relative to what I had heard before I updated. Even for me, someone who's fairly used to very high sound quality, it was a dramatic step up -- I couldn't believe how much better this combination sounded.
Most noticeably, I could tell that the volume was significantly higher. Everything I played came in loud and clear, even with only a modest volume set on my DAC. The overall crispness and soundstage seemed to have improved many times over, as well. It seemed to bring out the best in the mastering job of whatever I listened to, and was even easier on the ears than the previous software versions. Also, most of the quirks that haunted me on older versions of Amarra were no longer a problem. Track skipping, "broken record syndrome," or seconds missing at the beginnings and/or ends of the tracks had pretty much vanished.
Fast-forward about month or so and I had pretty much gotten used to the higher quality, not affecting me as strongly as my first few exposures. I can, however, still appreciate the fidelity provided by this system. It's still the best I've ever heard music sound, and the more I get hooked, the more lower fidelity grates on my nerves.
All in all, you've got my recommendation on this combo, you'd be in for a real treat -- ear candy anyone? ;)