AudioSettings.driverCaps  

// Set the speaker mode to that of the system settings.

AudioSettings.speakerMode = AudioSettings.driverCaps;

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Example() {
        AudioSettings.speakerMode = AudioSettings.driverCaps;
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Example():
        AudioSettings.speakerMode = AudioSettings.driverCaps