Well if it's a "centre
channel speaker",from a surround kit, you should'nt have much problem placing it close to the tv, as centre channel speakers tend to have smaller magnets in them and are usually sheilded just for this particular use. Now if you are using a Giganormous PA speaker, cause you have it just laying around... well that's another story.
Could you run a
line level signal from your surround amp center channal output to the audio input on the tv? Then you'd just be using the built in speakers for the center channel. Or is it that this is a monitor only PLasma ?