No significant issues to this. There's a higher hunidity level as you
get closer to the top of the tank, but I think TVs are typically rated
to something like 85% non-condensing humidity, and tanks have fairly
tight glass covers on them anyways.
Try to position your tank a bit lower and closer to the wall, and put
the TV on a bracket to pull it away from the wall. Ideal would be to
have the TV front about 1/3 of the tank's width back from the tank
front, so you have access to the tank for cleaning & feeding, and the
focal depth is close (TV to the inside of the tank), and most of the
TV's light effects will not blast down into the tank freaking the fish
out.
The aquarium stand becomes a good place to install the centre speaker,
but try not to have it make mechanical contact as the vibrations will
mess with the fish's behavior.
Now as you watch TV, your fish will watch you, in the stroboscopic
effects of the TV's light intensity. ;~)
NetMax