I just realised before reading the replies that I'll have to write a second article just on setting up these programs, though they all come with instructions in some form or another.
In iTunes, there is, for example, a 10-band equalizer. However, that doesn't cover the entire audible spectrum very well. However there is a system EQ that can be accessed in any program that can call it. Play and Vox can as they enable the use of the Mac OS X built-in effects filters. In Vox, the second button from the left on the controller window opens the effects window. Clicking on "Add" pops up a menu under which is an "Apple" sub-menu with a list of AUwhatever filters. AUGraphicEQ is the one you want. You can draw curves with it by holding down the control key and literally drawing a curve, the sliders jumping to the mouse location as it passes over. In Fedelia, the main window has three menus below the playback controls where effects can be added.
gzone3lement: a .plist file is a property list (a set of preferences for something) rather than the driver itself. I'm not sure that there is anything wrong with CoreAudio as such, especially as over the years Apple has improved it. However it may not be set up to get the highest fidelity out of the system. This is really a question we'd have to ask of someone who was writing one of these programs as to what CoreAudio could do better.
Thanks for the correction, Currawong. I'm glad CoreAudio improves over time. I'm not sure if there is anything wrong with CoreAudio either, but what I can say is that it is currently impossible to bypass it throughout the entire audio system.
Currently, I still use iTunes as of today. I personally like to double-click album artworks and select songs from there. I admire the idea of integration, and I see iTunes to be a stable, if not clean, program. so I probably will consider either Amarra or Pure Music. I have not tried out either products yet, but if I do hear difference in sound, I definitely will think about purchasing either one in the near future.
For Amarra, "the licence either requires an iLok USB key or the software is locked to a single computer which can't be transferred." I normally restore my laptop either once or twice a year. If this is the case, I should get an iLok USB key, right? I just want to make sure.
I played around with iTunes equalizer today, and the sound did indeed change depending on frequency. When using equalizers, don't they decrease sound quality because of sound skewness? For Pure Music, I hear the software supports VST and and AAU plugins, so it is possible to use a software equalizer with Pure Music. Does anyone know such a software that takes advantage of the Mac's EQ?