Try a mono center speaker bleeding the signal from the left and right channels. You will need a mono amp and speaker with similar quality as your stereo setup. You will be surprised what you have been missing when you gradually turn up that center speaker. It's like realizing that you have a blind spot in your field of view that you've had all your life but never knew it until you did the simple sight test to demonstrate the empty area. Once you have the center speaker, you will be able to separate the other two and widen your sound stage.
