A 'remote control' for the CD-ROM drive
CDPlayer is like a remote control for the CD-ROM drive. It completely by-passes Haiku's media services. If your CD-ROM drive doesn't support that or its audio outputs aren't connected to speakers (or routed through your soundcard), you won't hear a thing...
Modern computers only rarely fulfill these requirements.
In that case you're better off mounting the CD in Tracker and use MediaPlayer to play back the audio files in its wav folder.