win10 Audio 5.1 channel config - winapi

Question

I'm trying to change the channel set(like stereo to 5.1), but every api I tried just failed.
Like IDirectSound8::SetSpeakerConfig which now is NOP, according to microsoft.
now I'm trying IAudioChannelConfig interface, but somehow it failed again.
it just returns E_NOINTERFACE.
here's part of my code.
HRESULT get_chann_interface(IMMDevice *pEndpoint)
{
HRESULT hr;
PROPVARIANT *pActivationParams = NULL; // set to NULL to activate IDeviceTopology
IDeviceTopology *dev_topo;
hr = pEndpoint->Activate(IID_IDeviceTopology, CLSCTX_ALL, pActivationParams,(void**)&dev_topo);
if (hr < 0 || dev_topo == NULL)
{
err_out("IDeviceTopology activate failed: ", hr);
exit(hr);
}
IConnector *iconn;
hr = dev_topo->GetConnector(0, &iconn);// there is only 1 connector in the device topology
if (hr < 0)
{
err_out("IConnector interface get failed: ", hr);
exit(hr);
}
IPart *ipart;
hr = iconn->QueryInterface(IID_IPart, (void **)&ipart);
if (hr < 0)
{
err_out("IPart interface query failed: ", hr);
exit(hr);
}
IAudioChannelConfig *ichann_config;
hr = ipart->Activate(CLSCTX_ALL, IID_IAudioChannelConfig, (void **)&ichann_config);
if (hr < 0)
{
err_out("IAudioChannelConfig interface Activate failed: ", hr);
return(hr);
}
DWORD pdwConfig;
hr = ichann_config->GetChannelConfig(&pdwConfig);
if (hr<0)
err_out("GetChannelConfig failed: ", hr);
else
cout<<"channel config:" << hex << pdwConfig << endl;
SAFE_RELEASE(ichann_config)
SAFE_RELEASE(ipart)
SAFE_RELEASE(iconn)
SAFE_RELEASE(dev_topo)
}
I just failed to activate IAudioChannelConfig interface.
anyone knows any reasons?
thanks in advance.