i really dont have any expertise knowledge, but i would have to agree with bren. the air blowing directly from the vents can be anywhere from 45F to 55F degrees, and would make for extreme temp changes up and down the tower. now, i dont think that will effect the speakers themselves, but it could have adverse effects on the structure of the box and the veneer. the possibilities of it warping and pulling greatly increase.
this is all speculation on my part.. i would write an email or call the 1-800# for axion, and get their opinion.
EXCUSE ME, ARE YOU THE SINGING BUSH??