MSI GS70 STEALTH PRO (GTX 970M) - Manual (Page 20)

Introductions
2-12
7. Audio Port Connectors
Make high quality sound blaster with stereo system and Hi-Fi function supported.
Headphone out/ SPDIF-out
Š Used for speakers or headphones. The S/PDIF connector is
also provided for digital audio transmission to external
speakers through an optical fiber cable.
Š Connect the Front speakers here.
Line In
Š Used for an external audio device.
Š Connect the Rear speakers here.
Microphone
Š Used for an external microphone.
Š Connect the Center and Subwoofer speakers here.