Through hacking, a number of discoveries have been made about Sonic Adventure DX: Director's Cut.
There are a number of unused objects in the game. These objects include a button (Aoki Switch) in Lost World, tumbleweed in Windy Valley, trash can in Speed Highway, and icicle in Ice Cap. Dude discovered these in the PC port of SADX. The tumbleweed in Windy Valley could be accessed by changing the graphic quality to the highest in the Settings screen during the autorun.
If the player enters and exits the Casino area, copies of the casino geometry will appear at their global location. This can be seen by using debug mode to leave the playable area. It is believed that earlier in the production of Sonic Adventure, the adventure fields were intended to be one entire segment, instead of being split into several separate segments. This duplicate Casino geometry data is evidence that the adventure fields were originally meant to be one entire segment, but then segmented during production for efficiency. This Casino geometry data has incorrect textures, as it has erroneous texture references. It will frequently revert between textures, and sometimes even animate them.
By using the Action Replay moon jump code to enter the Station Square hotel early as Big, the door to Emerald Coast will be locked. However, keys similar to the Wind Key or Ice Key will be found by the door. When placed in their appropriate sockets, the door will unlock. flarn2006 discovered this. In addition, Member, Glisp has found information on the web from another source that allows the player to get into the hotel without an Action Replay, via a glitch involving Station Square's boat docks and the Hamburger Statue. He has made a youtube video to confirm this source correct which can be found here. Interestingly, if the player decides to access Emerald Coast early then they will go through the game as normal beyond that point. However upon beating Hot Shelter, the player will be transported to the past and stuck there permanently if the game saved. Sadly though, Big's name will be grayed out in Trial mode which means he will not be able to play in other character's levels. This is because the other characters that were able to do this, needed to have the first and second stage beaten followed by a cinematic within an enclosed space, such as Tikal's memories or areas that are locked at the start of the game (such as the Casino area). However since Big is required to access the beta hotel anytime before beating Ice Cap, (otherwise the Hotel will be as normal) he doesn't have that same circumstance as the other characters (which are Knuckles and Tails) that can do this.
The door in the Mystic Ruins that Sonic, Knuckles and Gamma pass through to access the Master Emerald shrine and Red Mountain has an opening/closing animation as well as being fully textured on both sides. Unfortunately, through regular means it is impossible to view any of this ingame as the door is only seen from one side and never seen opening/closing to any of the characters.
Story Screen Scripts: