I use my Mac for most music playback through my DecGear. So how many volume controls/music modifiers are there? I am still finding them.

System volume
iTunes Volume
EQ
iTunes Preamp setting
Alert Volume (so your system alerts don't blast you when listening to music louder than is perhaps necessary)
Crossfade

and finally

Sound Enhancer (iTunes Prefs) I just found this one, if you turn this on/up your instruments will get loud while vocals will go away.

Did I miss any?