To retrieve the capabilities of a capture device, call the IDirectSoundCapture::GetCaps method. The parameter to this method is a DSCCAPS structure. As with other such structures, you have to initialize the dwSize member before passing it.
On return, the structure contains the number of channels the device supports as well as a combination of values for supported formats, equivalent to the values in the WAVEINCAPS structure used in the Win32 waveform audio functions.