I created this script to tackle the biggest problem when combining FMOD and Oculus VR Framework --- FMOD's audio only outputs to the currently used system audio device and not mirror its output to the VR headset, unlike when using SteamVR.

FMODOutputUtils.cs

// FMOD Output Setter - Editor script
// Author: Made Indrayana
// MIT License
// Create a window in Unity to be able to explicitly select FMOD's audio output and auto enable it on every Play Mode.

using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEditor;
using FMODUnity;

namespace DoubleShot.Editor
{
    [InitializeOnLoad]
    public class FMODOutputSelector : EditorWindow
    {
        #region Variable Definitions
        private const string settingName = "DoubleShot.FMODAutoSetOutput.Enabled";

        private const string targetAudioDeviceID = "DoubleShot.FMODOutput";
        private const string targetAudioDeviceName = "DoubleShot.FMODOutput.Name";
        private const string numOfAvailableDevices = "DoubleShot.FMODOutput.NumberOfAvailableDevices";
        private const string availableDevicesConfig = "DoubleShot.FMODAudioDevices";

        private static bool isAutoFMODOutput
        {
            get { return EditorPrefs.GetBool(settingName, false); }
            set { EditorPrefs.SetBool(settingName, value); }
        }

        EditorApplication.CallbackFunction callback;
        #endregion

        #region JSON Class
        [Serializable]
        public class DeviceConfig
        {
            public List<int> ids;
            public List<string> names;

            public void Init()
            {
                ids = new List<int>();
                names = new List<string>();
            }
        }
        #endregion

        #region Helper Function
        private static bool isCurrentUsedDevice(int deviceID)
        {
            if (EditorPrefs.GetInt(targetAudioDeviceID) == deviceID)
                return true;
            else return false;
        }
        private static void SetAudioDeviceToDefault()
        {
            EditorPrefs.SetInt(targetAudioDeviceID, 99);
            EditorPrefs.SetString(targetAudioDeviceName, "Default System Device");
        }
        private static void GetNumAudioDrivers()
        {
            int i;
            RuntimeManager.CoreSystem.getNumDrivers(out i);
            EditorPrefs.SetInt(numOfAvailableDevices, i);
        }
        private static void ListAudioDevices()
        {
            DeviceConfig config = new DeviceConfig();
            config.Init();
            for (int i = 0; i < EditorPrefs.GetInt(numOfAvailableDevices); i++)
            {
                string name;
                Guid guid;
                int systemrate;
                FMOD.SPEAKERMODE AudioSpeakerMode;
                int speakermodechannel;
                RuntimeManager.CoreSystem.getDriverInfo(i, out name, 100, out guid, out systemrate, out AudioSpeakerMode, out speakermodechannel);

                config.ids.Add(i);
                config.names.Add(name);
                EditorPrefs.SetString(availableDevicesConfig, JsonUtility.ToJson(config));
            }
        }
        private static void OnAvailableAudioDevicesChanged()
        {
            if (EditorPrefs.GetString(targetAudioDeviceName) == "Default System Device")
                return;
            else
            {
                DeviceConfig config = JsonUtility.FromJson<DeviceConfig>(EditorPrefs.GetString(availableDevicesConfig));
                if (config.names.Contains(EditorPrefs.GetString(targetAudioDeviceName)))
                {
                    int id = config.names.IndexOf(EditorPrefs.GetString(targetAudioDeviceName));
                    EditorPrefs.SetInt(targetAudioDeviceID, id);
                }
                else
                {
                    Debug.LogWarning("Previous audio device not found, reverting back to default!");
                    SetAudioDeviceToDefault();
                }
            }

        }

        #endregion

        #region Method run on entering Play Mode
        [RuntimeInitializeOnLoadMethod]
        private static void SetOutputToDriver()
        {
            if (isAutoFMODOutput)
            {
                if (EditorPrefs.GetInt(targetAudioDeviceID) == 99)
                    RuntimeManager.CoreSystem.setDriver(0);
                else
                    RuntimeManager.CoreSystem.setDriver(EditorPrefs.GetInt(targetAudioDeviceID));
            }
        }

        #endregion

        #region Window Menu Item and initializer
        [MenuItem("Double Shot/FMOD/Output Selector", false, 0)]
        private static void Init()
        {
            if (!EditorPrefs.HasKey(targetAudioDeviceID))
            {
                SetAudioDeviceToDefault();
            }

            GetNumAudioDrivers();
            ListAudioDevices();
            OnAvailableAudioDevicesChanged();

            FMODOutputSelector window = (FMODOutputSelector)GetWindow(typeof(FMODOutputSelector), false, "FMOD Output Selector");
            window.Show();

        }
        #endregion

        #region OnGUI
        private void OnGUI()
        {
            GUI.skin.button.wordWrap = true;

            GUILayout.Label("Automatic Output Selection", EditorStyles.boldLabel);
            isAutoFMODOutput = GUILayout.Toggle(isAutoFMODOutput, "Enable");


            GUILayout.Space(10);

            GUILayout.Label("Audio Devices", EditorStyles.boldLabel);
            PrintAudioDevices();

            GUILayout.Space(10);


            if (GUILayout.Button("Refresh Audio Devices List", GUILayout.Height(50)))
            {
                GetNumAudioDrivers();
                ListAudioDevices();
                OnAvailableAudioDevicesChanged();
            }

        }
        private static void PrintAudioDevices()
        {
            // Print Default Device
            if (GUILayout.Toggle(isCurrentUsedDevice(99), "Default System Device"))
            {
                SetAudioDeviceToDefault();
                if (EditorApplication.isPlaying)
                {
                    RuntimeManager.CoreSystem.setDriver(0);
                }
            }

            // Print specific audio devices
            DeviceConfig config = JsonUtility.FromJson<DeviceConfig>(EditorPrefs.GetString(availableDevicesConfig));
            for (int i = 0; i < config.ids.Count; i++)
            {
                if (GUILayout.Toggle(isCurrentUsedDevice(i), config.names[i]) && EditorPrefs.GetInt(targetAudioDeviceID) != i)
                {
                    EditorPrefs.SetInt(targetAudioDeviceID, i);
                    EditorPrefs.SetString(targetAudioDeviceName, config.names[i]);
                    if (EditorApplication.isPlaying)
                    {
                        if (EditorPrefs.GetInt(targetAudioDeviceID) == 99)
                        {
                            RuntimeManager.CoreSystem.setDriver(0);
                        }
                        else
                        {
                            RuntimeManager.CoreSystem.setDriver(EditorPrefs.GetInt(targetAudioDeviceID));
                        }


                    }


                }
            }
        }
        #endregion
    }
}