Magnets won’t in any way damage tape heads. Magnets can affect a recording on a tape (re-arrange the tiny magnetic particles) but tape heads will in no way be damaged by a magnet from a speaker. That said it is not a good idea to have any magnets near tape heads because if a magnet is strong enough and close enough -magnets can affect recordings.
What I would be worried most about is the weight of the speaker on top of the unit. This can throw out of alignment the DVD tray and the VCR tape mechanism. Maybe even stop heat from escaping and damage the unit from overheating.
What I would be worried most about is the weight of the speaker on top of the unit. This can throw out of alignment the DVD tray and the VCR tape mechanism. Maybe even stop heat from escaping and damage the unit from overheating.