MSI 815 PRO Manual page 40

This jumper is used to enabled/disabled Onboard Software audio, for
enabling AMC97 on AMR slot. Note: This jumper will only exist if there's no
Hardware audio onboard.
1
JP3
JP4
Note: Short pin 2-3 on JP4, to be able to use AMR card.
3
Enabled Onboard Audio
Enabled AMC97 on AMR(Audio
Modem Riser) Card
2-36
Function