You'll probably want to set up your mesh Wi-Fi kit in bridge mode. Most support this mode, which means that devices connected to the mesh Wi-Fi network can communicate with wired network devices connected to your existing router.  It also reduces the chances of running into problems when playing online games or hosting your own game server.  If you don't use bridge mode you might find you can’t do things such as print from a PC that's connected to your exiting router to a wireless printer. The disadvantage of using bridge mode is that it tends to prevent you from using many of the mesh system's features such as parental controls, pausing Wi-Fi and others.