Well I tried it last night, looks like it does the trick and doesn't have any effect on the TV (that I can see).
Prior to having the speaker on top of the TV, I had it about 1 foot behind and 1 foot above the top of the TV on top of the fireplace landing thingy.
I am not sure what to think about the centre now, I think I preffered it up top on the fireplace. The M3 has a very nice response for vocals, very nice low end, it is not "thin" by any means and can handle any type of vocals with clarity and depth (although I have yet to try tree beard for the true test).
In the end, I don't think the sound was changed much from switching the tweeter to the bottom.
