do you have the basic stock system or does it say Infinity somewhere in the vehicle? Chances are you have an external amp that runs the speakers and will need to hook up your remote wire to turn on the factory amp. Unfortunately if this is the case, it won't sound any better than the stock radio and in some cases will sound worse unless you bypass the factory amp.
So the second option would be, if you have a factory external amp, is to bypass that amp by running all new speaker wires or using a bypass harness at the amp itself.
If you don't have an external amp, try hooking up a speaker directly to one of the speaker outs on the radio to make sure the radio internal amp isn't blown. Also, make sure all your wires are correct for the speaker connections