Hi @sjcindustries . What type of NBN connection do you have?
You should investigate if you can use a longer ethernet cable (Cat6) between NBN box and router. Depends on the layout of the house. It would mean the wifi is not being wasted in the garage. And ethernet would be available inside house.
Phone and coax cables can't be used to connect devices to the router.
Extenders and mesh units need the wifi signal from the riuter. Some mesh units have ethernet ports but still use wifi connection back to router.
@sjcindustries . If it is only a short distance, what signal strength and wifi connection speed does the Xbox get with just the router? It is unlikely to be as fast as the gigabit ethernet port but should be fast enough for gaming. The 5G band gives better speed over short distance. The 2.4G band has longer range with lower speed. An extender will extend wifi coverage past the media room but is still limited by the wifi speed of the router.