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Thanks for asking.
The volume and other special keys are not handled by the OS X keyboard input infrastructure, but rather a few levels higher in the hierarchy on the HID level. They can therefore not be emulated.
As long as you're not running other software that wants to access the Apple Remote, you can, however, use Remote Buddy's Virtual Remote's Up/Down actions to emulate up / down presses of an Apple Remote, to which OS X reacts by bringing up the volume display. It does so only while you're not using other software that wants to use the Apple Remote, though. If you do, that software will react to your button presses accordingly.
Best regards,
Felix Schwarz