No worries at all. A plasma TV isn’t affected by magnetic fields, so it can be as close to your center channel as you want.
The old tube TVs have a phosphor screen on the front and get electric rays (simple explanation) shot at it from the back of the set to excite them and give off the right colors in the right places. The phosphor is affected by magnetic fields that speakers have as a byproduct of their large magnets that they use. So that`s why we have to use shielded speakers as center channels on older tube TVs.
Plasma, LCD, rear projection or front projection type screens are not affected by standard speakers.
How far away from my 42″ plasma does a JBL HTI 6 unshielded in wall, used as a center channel, have to be so it will not cause problems.
Jack Kress, San Diego