The important item is to open up the back of the unit so this shelf is accessible from the back of the unit. This opening is needed not only to place the center channel in the unit but for the proper acoustics. Building speakers into an entertainment unit is something that can be very tricky, and only should be done after the acoustics of the room in which it to be placed is determined. The size and design of the speakers themselves play a very major role in the placement. Zero One's require a placement of 26 in from the floor and no closer than 3 feet to the side for proper imaging.
Improper placement can result in a video system that is unsatisfactory.
As an experienced amateur wood worker and a audio buff I often get requests from friends and acquaintances to recommend or build entertainment centers. I have built 5 so far with good results. The most recent was one for family which had to be moved in the back of a short bed pick-up truck 800 miles and could not extend above the top of the cab of the truck. The unit was 60 in wide and 66 in tall and ended up being 6 pieces. I've just recently completed a traditional style wood kitchen in maple.