Which Audio?

DefCon1

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Nov 25, 2011
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I have a Gigabyte GA-Z68X-UD3H-B3 (Rev 1.3) motherboard. The manual says:

"The front panel audio header supports Intel High Definition audio (HD) and AC'97 audio. You may connect your chassis front panel audio module to this header."

The front panel cable on my Cooler Master HAF X case ends in two plugs: one "ALC97" and one "HD Audio".

Nowhere can I find an explanation of the difference between the two! So - what IS the difference between the two, and which plug goes into the header for plugging in a mid-quality stereo headphone?