can, or should, you put your center channel on top of your sub?  anything you need to do?  would it vibrate the center too much?  need insultation or some type of barrer?  here is a pic just in case......

btw....i am kicking around the idea of making an et cabinet so there is not visible equipement in the living room.  i think it would be a cool idea.  the pic is what the living room would look like.  any precautions i need to know if i am going to do something like this?  i already realized if i am going to use a surge protectior (furman 15pfi) that my tv and subs won't be pluged into them.  well unless lg and ed will make my stuff with a 20' power cord..... 

 Depends on sub,opposed firing subsdo not vibrate(cabinet),subs like the very compact Sinfire with a PR are the worst case(they do the sub dance when pushed).

On most subs you can place a center with no problems,I use rubber pads so the center channel is isolated a bit and does not slide. 

should be fine. the surrounds should not be placed like in the picture though. they should be placed exactly or close to possible to the left and right of your ear