March 20, 2013
On 3/20/13, Andrej Mitrovic <andrej.mitrovich@gmail.com> wrote:
> It seems to be COM-based, so it should be usable from D.

Actually slight correction, for example the endpointvolume.h header in the Windows SDK defines both a COM and a C API, but the COM API is probably easier to use.
March 21, 2013
On 3/20/13, Andrej Mitrovic <andrej.mitrovich@gmail.com> wrote:
> It seems to be COM-based, so it should be usable from D.

Apparently there aren't any. Anyway I've ported the basic Core Audio sample to D, which has a slider for the main volume and a mute button:

https://github.com/AndrejMitrovic/DSoundMan

It includes some prototypes for Core Audio.

P.S. Yeah I know Apple uses CoreAudio, I don't know why MS decided to use the same name.