OK, the spring (it looks like a "^") in the bottom of the center vent needs to be pushed down until it releases the vent unit. Then, there are four tabs that pop into holes that must be forced out by pushing from behind (by reaching in where the MCS unit sits). I also used a plastic putty knife to pry from the front. Then, it just pops free!

(P.S. to remove the radio (MCS): This takes about a minute with the removal "keys". I made my removal keys in about 20 minutes after looking at a picture on ebay and cutting them out of a piece of scrap metal.)