Do you have a cable connecting your CD drive to your soundcard CD In port? If not, you either need to get one, or enable digital playback in your cdplayer.
Normal playback basically starts the cd in play mode, and the audio is sent through an analog wire to your soundcard directly. For digital playback mode, each track is read digitally, and the data is sent to the soundcard's pcm via the system busses. Little more cpu intensive (not enough to worry about though), but it is easier to build a system this way (less wires).
You didn't list which Redhat version you were running, so it may not be possible if you are running an older version. You could install xmms, and use it's cd playback capabilities. It does have an option for digital playback.