I see that Windows Media Player WMPLib library has WMPEqualizerSettingsCtrl class among its exported classes, but I can't find any info about using this class. Is there any dedicated public source of documentation about WMPLib in general or at least about using WMPEqualizerSettingsCtrl? On MSDN I found only info about several individual classes from WMPLib and nothing at all about WMPEqualizerSettingsCtrl.
This interface is not intended to use via COM by applications. It is restricted to skins and is available only for skin creators. For Windows Media Player skin programming reference (equalizer in particular), check out this MSDN topic.