Magnetic fields do not affect these types of sets since they do not use a beam or phosphors but static liquid crystals, which are solid-state unmoving cells. Although they are still sensitive to electric field changes, it would take substantial effort for you to ruin the display. Even then, it would be have to be done willingly.
Moreover, projection displays do not have shadow masks and hence this type of damage does not apply.
Therefore, you should not worry about placing speakers next to LCD and plasma TV’s or about placing a television near any other kind of appliance with a magnet in it, since magnets do not harm them.