When you use DVD Player to play a movie in Mac OS X 10.4 Tiger, you won't be able to adjust the digital audio output volume (a feature on some Power Mac G5 and iMac G5 computers) in DVD Player. Also, adjustments to the Audio Equalizer settings while playing a movie in DVD Player will have no effect on digital audio output.
Although you can move the DVD Player volume slider, only external analog speakers and built-in speakers respond to the volume change.
If you need to adjust the volume on your digital output, use the volume control on your external digital audio device instead.