What player skins are you referring to?


I'll let Wilbert handle this but I do see in the documentation for the mediaplayer class that the volume can be set

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soundTransform property

soundTransform:SoundTransform [read-write]

A SoundTransform object can be assigned to the soundTransform property to set volume and balance.
Implementation
public function get soundTransform():SoundTransform
public function set soundTransform(value:SoundTransform):void