OK, while the Z-680's set to PLII Movie Mode, have the game (zelda/metroid) loaded up. While you're in the game world (not the main menu) press Start and find the Options menu, and adjust the audio settings. You'll usually find a set of choices like Mono / Stereo / Surround, or Mono / Stereo / DPLII. Other games have their audio options accessible only from their main menu (example, Burnout 2).
One exception would be Star Wars: Rogue Leader, where its "Stereo" option counts for both Stereo and DPLII mode.