I have 4 invisa MPX speakers that I'm using for surrounds, I am placing them in columns that are 12x6x8... I have insulation in the bottom half of the columns and was wondering if I should place insulation in the top half of the columns behind the speakers themselves?

thanks

It might not make a large difference, but adding some insulation directly behind the MPX won't hurt. Just make sure the insulation is not compressed much so it will do its job better.

Thanks for your reply!
I just didn't want the insulation to dampen the sound too much at the same time I don't want it to sound like a hollow box as well.

You should be fine, no problem.