Digital cable for CD/DVD-Rom

OK,

I’m kind of confused. I currently have my DVD-Rom connected to my Sound Blaster Audigy through a digital cable (the small connector). When I play a DVD the Dolby Digital Light on my speaker console comes on. If I disconnect the digital cable and play a DVD, the light still comes on. Is the Dolby Digital stream or the digital stream for that matter running through the digital audio cable or the IDE cable?

What is the purpose of this cable? Do I need it if the Dolbly Digital signal travels through the IDE cable?

Is it actually made for playing CDs? Should I use the digital audio cable to connect my CD-Rom to the soundcard?

DVD Audio (any type) goes through the IDE cable. The only time that the Digital or Analog audio cables are used is when you are playing an audio CD.

I thought it was something like that…thanks…