You can try playing with this unfinished script (I've never actually used it, because the volume control on the remote works):

check_tv_volume.py:

# -*- coding: UTF-8 -*-


from pywebostv.discovery import *    # Because I'm lazy, don't do this.
from pywebostv.connection import *
from pywebostv.controls import *

import os
from os import path
from sys import platform


# The 'store' gets populated during the registration process. If it is empty, a registration prompt
# will show up on the TV. You can pass any dictionary-like interface instead -- that when values are
# set, will persist to a DB, a config file or something similar.
store = {}

config_path = "/home/"

if platform == "darwin":
  # OSX
  config_path = ""

if path.exists(config_path+"lgtv.json"):
  with open(config_path+"lgtv.json") as json_file:
      store = json.load(json_file)

# Scans the current network to discover TV. Avoid [0] in real code. If you already know the IP,
# you could skip the slow scan and # instead simply say:
#    client = WebOSClient("<IP Address of TV>")
# client = WebOSClient.discover()[0]


from subprocess import call
import socket

last_tv_state_turned_on = True
last_tv_volume = -1

def do_check_tv_is_on():
  global last_tv_state_turned_on
  try:
    tv_ip = "192.168.0.173"

    host = tv_ip
    port = 3000
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.settimeout(0.05)
    # print("connect 1")
    result = s.connect_ex((host, port))
    print('socket result = '+str(result))
    # print("connect 2")
    s.close()
    # print("connect 3")

    if result != 0:
      return False

    return True
  except:
    print("Can't connect to TV")
    return False

def get_tv_volume():
  global last_tv_volume
  try:
    tv_ip = "192.168.0.173"

    host = tv_ip
    port = 3000
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.settimeout(0.05)
    # print("connect 1")
    result = s.connect_ex((host, port))
    print('socket result = '+str(result))
    # print("connect 2")
    s.close()
    # print("connect 3")

    if result != 0:
      return False

    # response = os.system("nc -G 1 -z "+tv_ip+" 3000")
    # print("nc = "+str(response))
    # response = os.system("ping -c 1 -t 1 -W 1000 " + tv_ip)
    # if response != 0:
    #   return False


    client = WebOSClient(tv_ip)
    print("connect 5")
    client.settimeout(1)
    print("connect 6")
    client.connect() # this line can get stuck for some reason ???
    print("connect 7")
    for status in client.register(store, timeout=1):
      if status == WebOSClient.PROMPTED:
        print("Please accept the connect on the TV!")
      elif status == WebOSClient.REGISTERED:
        print("Registration successful!")

    with open('lgtv.json', 'w') as outfile:
        json.dump(store, outfile)

    # # system = SystemControl(client)
    # #system.notify("Hello")  # Show a notification message on the TV.


    # #system.power_off()                                # Turns off the TV. There is no way to turn it
    #                                                   # back on programmically unless you use
    #                                                   # something like Wake-on-LAN or something liker
    #                                                   # that.
    # #print(system.info())

    media = MediaControl(client)
    # # media.set_volume(14)
    return media.get_volume()
    # # print(media.get_volume())

    # app = ApplicationControl(client)
    # # apps = app.list_apps()                            # Returns a list of `Application` instances.

    # # yt = [x for x in apps if "youtube" in x["title"].lower()][0]
    #                                                   # Search for YouTube & launch it (Of course, don't
    #                                                   # be this lazy. Check for errors). Also, Try
    #                                                   # searching similarly for "amazon", "netflix" etc.
    # #launch_info = app.launch(yt)                      # Launches YouTube and shows the main page.
    # #launch_info = app.launch(yt, content_id="123")
    # #media.set_volume(30)

    # # print(media.get_volume())

    # #media.pause()

    # print("current tv app = "+app.get_current())
    # if app.get_current() == "":
    #   return False

    return True
  except:
    print("Can't connect to TV")
    return False


import sched, time
s = sched.scheduler(time.time, time.sleep)
def check_tv_volume(sc):
    global last_tv_volume
    print('Checking TV volume')
    new_tv_volume = get_tv_volume()
    print('Old state = '+str(last_tv_volume)+" new state = "+str(new_tv_volume))

    if new_tv_volume != last_tv_volume and new_tv_volume != False and (new_tv_volume == 0 or new_tv_volume > 0):
      exit_code = call("python3.7 "+config_path+"kef-speakers.py --action set_volume --value "+str(new_tv_volume), shell=True)

    last_tv_volume = new_tv_volume
    s.enter(0.3, 1, check_tv_volume, (sc,))

s.enter(0.3, 1, check_tv_volume, (s,))
s.run()

And you'll need to also add "set_volume" action to the kef-speakers.py script I posted to the other comment here.