Built-In Cabinet with Components Installed in Center Area
This is a built-in cabinet system with components installed directly below the TV which is between cabinets to the left and right.
While heat can definitely accumulate and cause problems, this is a relatively easy fix. One additional note is that in the image with the doors open, that is all one area as there is no divider between the components. Another 'to do' is to cut holes to provide airflow between the shelves. In this case, since the shelves cannot be removed, several 3" holes in the back of the shelves should be sufficient. It is very important to facilitate natural airflow.
Solution to the Situation:
The best solution is to simply vent to the side cabinets. The heat from components by all accounts is just considered 'warm' air as it's not going to start a fire or damage the cabinetry. Because of this, venting to the side cabinets that do not house components will work fine. Using a Cabinet Vent or Slim Vent Package, you can vent to both the left and right cabinets very easily and effectively. If there will be several heat producing components, beyond just a receiver, cable or satellite box, and DVD player, then HiFlo Lite units may be better suited for the application.
The other option is to vent through the top of the cabinet and in this case, behind the TV. This is a very easy solution but you will then have a grill on the top area of the cabinet to contend with.
You also should not be overly concerned about air entering the cabinet. A lot of air can enter between the cracks in the doors unless the doors are very tight. In this application, the doors actually are pretty tight so a Cabinet Toe Kick System may be used if that is an issue. To install, simply cut the long narrow grill into the toe kick and then install the Cabinet Vent that comes with the package into the bottom of the cabinet. This will pull plenty of fresh air into the cabinet.