I'm not sure, my first thought was that it may effect the cones ability to work as intended due to the extra magnetic pull. You could try putting a non magnetic shield between the two. Just guessing. You could try it out of the box to see what difference, if any, there is.
It would have to be an awful thin one, like a coat of paint on the back of the magnet.
will the enclosure be vented?
what size are the speakers?
if not vented then when both cones move forward they will create low pressure in the enclosure and when the cones both move inwards then they will compress the air between them. this will affect the sound . Adding a vent will let the speakers move air in and out so they dont work as hard..or against each other.
its fine if there is enough volume of air in between the speakers but if they are so close they are touching ??
try it and see if you like the tone. if its ok to you then thats all that matters.
Yes, 2". I determined last night though that there is enough room between the magnets for a piece of aluminumthick enough that it seems to isolate them. I'll try and see what happens.