the face of Honda decks is slightly larger than a single DIN face... but is ROUGHLY the size of an aftermarket DIN headunit WITH the trim ring. An aftermarket DVD player can be fit below the stock radio, you'll just have to trim the trim ring for the new player, or make a custom one.

For the Odyssey, there is a lower dash/console piece that has a DIN opening, it is used in the Odyssey when the optional DVD system was installed. Just so you know, in case you want to "conceal" the dvd player more, as its much harder to see down there.