AUXDM_GETVOLUME

Sent to an auxiliary audio device driver to request the current volume level setting for a device.

The return value is an error code, or zero (MMSYSERR_NOERROR) if the operation is successful. Possible error codes are:

MMSYSERR_NOTENABLED	The driver failed to load or initialize.
MMSYSERR_NOTSUPPORTED	Function isn't supported.

DWORD dwParam1: Specifies a far pointer to a DWORD location. The driver fills this location with the current volume level setting. The high-order word contains the right channel setting and the low-order word contains the left channel setting. A value of 0 is silence, and a value of 0xFFFF is full volume. If the driver does not support both left and right channel volume changes, it returns the volume in the low-order word.
DWORD dwParam2: Unused.

Drivers do not have to support volume level changes. However, if a driver supports changes to the volume level with the AUXDM_SETVOLUME message, it must support queries with the AUXDM_GETVOLUME message.