Gigabyte GA-8TX User Manual page 62

e. Click "Digital" item, Line Out will be reconfigure to SPDIF Out.
f. Recommend you to select "Autosense", It will automatically detect the type (mono or stereo)
of the audio connector that you plug into Line Out audio jack, then configure Line Out to
either SPDIF or Speaker accordingly.
Four Speaker & SPDIF Introduction
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