I'm sorry to have to tell you this, but your information is out of date. What you are saying USED to be true (past tense), but is no longer true. If you play a DVD in your computer, in your Nec 3520A, using PowerDVD running under Windows XP, all of the data (video and audio) goes down the IDE cable. PowerDVD then decodes the audio and passes it to the sound card.
Think about this: If you rip the files to your hard drive, and then play them using PowerDVD, how do you think it works? Now don't you think PowerDVD does the SAME thing when playing from the Nec 3520A?