if your inside the netherrealm city, but it says A-8, that may be the problem. go outside the city and up to A-4, then go as far west as u can and look south. you will notice that you can travel along the outside the western wall of the city all the way down to A-8, there is a gold chest there that i opened a long time ago, so i cant remember for sure whats in it. but if you haven't been down that way, id say its a good bet. because i've opened every chest in konquest mode, and as far as i can tell, that is the only gold chest in A-8 NetherRealm.