Asus PCI Express Audio Card Xonar DX User Manual page 32

6.2.4 Audio Channels (For Vista only)
This setting only appears in Windows Vista. Vista will deliver the audio channels
to the audio driver according to this setting, no matter what the original audio
content is or how many channels they have. Therefore, you need to set this in
accordance with your audio content before you play it. Please note that this setting
is synchronized with Vista's system speaker configuration and changing the
setting during playback will cease the audio playback program. You may have to
restart the program after the change. It's recommended that you close all playing
programs before you change the setting.
No Item
1 Audio Channels
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Description
Here are some typical suggestions:
-MP3, WMA, AAC, CD, VCD, 2D games => 2 channels
-DVD-Video with Dolby Digtial or DTS 5.1 => 6 channels
-DVD-Video with Dolby Digtial EX or DTS ES => 8 channels
-3D games => 8 channels
ASUS Xonar DX