There is the 'master volume' which adapts to the media being played, and there are the 'mixer volume' controls which deal directly with the soundcard (and do update when you change the volume elsewhere). When QCD is using the WaveOut plug-in, modifying the WAV volume from the system level affects QCD's volume. When you switch to the DirectSound Crossfading plug-in, QCD doesn't respond at all when you modify the WAV volume. Go into Preferences->plug-ins->Playback and check one of the DirectSound plug-ins instead of WaveOut. If you select the Crossfading plug-in, you will need to go into its configuration, then on the 'Device/Buffer' tab uncheck the 'Adjust volume on primary buffer' option.