I must still upload the Chao Gardens and Characters mod, and meanwhile here is for now the download for the latest version of SADX99 mod. Note that it may have some things that could interfere with the latest mods, and it basically won't be "supported" anymore after this.
EDIT: Deleted outdated mod, look below for the good stuff
Here are the current links for all the relevant mods and tools in this:
Dreamcast Branding (TheArcadeStriker, PkR, JCF)
Restores the original Title Screen, as well as DC buton prompts in Chao Garden and Tutorials, HUD, and other things. (Currently must also restore the DC credit screens)
SADX Dreamcast conversion (PkR)
It's function is to edit the palette/PL BIN files in the Dreamcast/Gamecube proto version.
Dreamcast Sub Games (TheArcadeStriker)
Restores the landtables for Sand Hill and Twinkle Circuit, adds DC textures for Sky Chase
Dreamcast/Palette lightning mod (Morph/SF94)
There could also be updated stuff at the latest pages of this topic, so you can also go check there for more information (Specifically in SADX Dreamcast conversion).
HUGE thanks to PkR for the collaborations, help, and the many things he has done currently, MainMemory for all the awesome mods and hacking done for SADX, as well as the help it gave to me, ItsEasyActually and Morph for all the awesome stuff they have done (and the DC lightning mod), and JeffCharizardFlame & CheatFreak for the intro movie and the code to disable the Sonic Team logo in the DC Branding mod.