Center channel questions

I currently listen to my TV sources using a normal two channel stereo. Its very high end but my wife and I often cant understand dialog and other times the sound track background noises and music overwhelm the dialog. Is this because we are missing the center channel information?

I understand the the center channel is dedicated mostly to voices so the addition of a center channel might clarify our problem.

If i am correct I would be looking for a center channel decoder. (I don't want to buy a 5.1 channel system, just a mono amp being driven by a center channel decoder if such a thing exists. Please comment and or make suggestions.