Amarra HiFi from Sonic Studio
Apple's iTunes is one of the best music libraries available but is lacks some key features required for hi-fidelity use. Amarra provides a very good solution that uses iTunes to store and organize the music while Amarra handles the "audiophile quality" issues.
The Mac Operating System was designed to allow many applications to play nice with each other; therefore one application is not allowed to change resources that are required by another application. The iTunes application for example is not allowed to change the core audio settings for sampling rate just because it senses a new file with a different sampling rate. Otherwise another application e.g. iMovie that may be using core audio at the time would crash or malfunction when iTunes changed the sampling rate. As a result iTunes will play all files (of different sampling rates) with the fixed sampling rate set by the "Audio Midi Setup" system application. The end result is awful sounding playback.
The manual override is to use "Audio Midi Setup" to set the sampling rate before starting iTunes and each time the music file selected is of a different sampling rate, you would quit iTunes, set the correct sampling rate with "Audio Midi Setup", then restart iTunes. Although you could automate this process somewhat, you would still be using Apple's core audio which was designed to be "all things to all people"; not the best solution.
The main features of Amarra HiFi are:
1. Provides automatic sampling rate switching (up to 192 kHz) without restarting iTunes.
2. Bypasses Apple's core audio and uses its own audiophile grade audio processing.
3. Sonic Mastering EQ that links to iTunes Equalizer. I don't recommend using the EQ feature since I found that the system consistently sounded better without EQ.
4. Easy FLAC to AIFF conversion. iTunes does not support FLAC playback so you have to convert the files to AIFF first. In theory this is actually a good idea anyway even if iTunes did support FLAC. Since AIFF files are uncompressed, the computer does less work playing back AIFF files. FLAC files on the other hand are compressed; therefore the computer has to un-compress them in real-time during playback.
Amarra HiFi cost US$49 and is really good value for money. The next level up is Amarra that cost US$189 but I think this would be an overkill for most applications. It does support sampling rates up to 384 kHz and has a more advanced Equalizer. It also has its own playback feature that makes iTunes optional. iTunes does a much better job organizing and interacting with the music library so I would not recommend going with this option.
The main problem I had with Amarra HiFi was unexpected crashes initially but this was quickly solved. I was upgrading from the older Amarra Junior and I had it in my "Login Items". This means that when I start the Mac Amarra Junior and Amarra HiFi were both trying to run and consumed a lot of memory. In this case I had less than 200MB of free memory. After deleting Amarra Junior from my "Login Items" and restarting the Mac, I had over 2GB of free memory and the system worked flawlessly afterwards.
There are other competing products available for the Mac such as Pure Music from Channel D. Some readers may like Pure Music, and from what I have read, it sounds decent. I find the user interface ugly and clunky and therefore I would not seriously evaluate it.
Overall, I really like Amarra HiFi and for the price you get audiophile quality playback in a clean tidy package. Amarra HiFi is available from Sonic Studio.