After going through Mac music players like a bag of chips, a new player I recently tried might just be my new reference player. Called Audirvana.
Pure Music still offers the best feature-set and overall usability - but I have been using AyreWave (now called Decibel) for my music playback. I found when comparing the two players, that the bass on Pure Music was more bloomy when compared to Decibel and that Decibel had more focus and sounded more natural in the upper freq.
Now, I recently tried Audirvana and it might be my new reference player. For strict music playback, it sounds amazing. Not sure if it all stems from how it uses the memory buffering or management, or what, but it sounds like it has more low-level detail, more "blackness" in the background, tighter bass (a lot more defined and tighter than Pure Music, slightly better than Decibel) and the vocal ranges and high freq. are amazing. Female vocals especially sounded more "real" than ever. I initially thought the high freq. might be a tad rolled off, but after some listening they sound crisp and quite impressive. It offers a fairly lack-luster feature-set when compared to Pure Music, but for strict listening, you should give it a try. I was impressed!

I'll have to do some more comparisons on more music, as I only have been listening to it for a few days, but the initial impressions are very good. It sounds like it isolates the sound from the rest of the operating system better than the other players.
Also, I had to turn off the "Audio Device exclusive access mode" option in the Preferences to get my Tranquility SE DAC to properly play music back. I think it was trying to play at the wrong freq. or something. It is similar to the direct-control in Pure Music, where it has direct-access to the playback device. I might have to play around with different settings to make this work, but it sounded fantastic with it off anyhow.
You can download it from:
http://audirvana.googlecode.comAnd there's some reviews and good discussion going on, over at:
http://www.computeraudiophile.com/content/New-OSX-Opensource-audiophile-player-AudirvanaFeature Set:* Native playing of FLAC, libSndFile (WAV, AIFF, ...), ALAC and other quicktime formats (AAC, MP3, ...)
* Direct sound path, directly to the CoreAudio HAL for pure bit perfect sound
* Audio Device exclusive access mode
* Automatic sample rate switching
* Up/Oversampling capability
* Plays completely from memory
* Tracks are loaded, decoded and sample rate converted in a memory buffer before being played
* Minimizing CPU and hard drive activity to lessen sources of interference
* Gapless playback by using a double buffering mechanism (playing track and next track)
* Transparent split load for loading tracks of any size
* Background tracks loading/decoding (including sample rate conversion)
* Playlist (m3u & m3u8 formats) load/save
* Handles Apple IR Remote
* Automated updates downloading (using Sparkle)
Upcoming features:* Dithering implementation, with tests on 16bit files improvement
* Scripting features for being controlled by Apple Scripts
* Tracks library with iTunes database access and folders crawling (mainly for FLAC)
* Remote control (through UPnP control point?)
* HAL I/O using DAC native physical formats (instead of CoreAudio 32bit float), but I don't have a DAC with such modes to develop this feature...
* Hardening playback in adverse conditions like OS swapping memory, ... that can cause clicks & glitches
* And bug fixes...