It is analog:
From page 26 of the PDF:
The audio subsystem supports the following features:
• Analog line-out/Analog Headphone/Analog Microphone (front panel jack)
It also has the pinout of the plug.
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It looks like the characteristics of the front panel analog port are part of the Intel HD audio specification for PCs:
You can get digital signals via the HDMI or Displayport connectors.