Volume Control Number of Channels XP different than Vista

MIXERLINE MixerLine;
memset( &MixerLine, 0, sizeof(MIXERLINE) );
MixerLine.cbStruct = sizeof(MIXERLINE);
MixerLine.dwComponentType = MIXERLINE_COMPONENTTYPE_SRC_WAVEOUT;
mmResult = mixerGetLineInfo( (HMIXEROBJ)m_dwMixerHandle, &MixerLine, MIXER_GETLINEINFOF_COMPONENTTYPE );