VirtualKeyboard API needs more control over sound effects

Currently, the Virtual Keyboard API accepts only a URL to specify a sound effect for a key in KeyPanel. This is very limiting, as it doesn't allow more fine grained control over the effect. Most prominently, it is impossible to control the volume of the effect. I tried several work-arounds, and the only workable one I could find was to have the application re-create the .wav file for the sound effect in code at the correct volume when changing the volume settings, which is rather hackish. 

It would be better if one could just use a SoundEffect instance instead, which would enable proper volume control (among other things).