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EDIT: Deleted outdated mod, look below for the good stuff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:
SADX Dreamcast conversion (PkR)
It's function is to edit the palette/PL BIN files in the Dreamcast/Gamecube proto version.
Dreamcast/Palette lightning mod (Morph/SF94)
The Dreamcast Sub Games mod was integrated in the Dreamcast conversion (and PkR added some fixes and things to it), as well as the DC Branding mod (and he did add some things too to it, it should have credit screens in the 25/01/17 update *wink wink*). The Sub Games mod integration is in the latest public version in Dropbox, while the DC Branding AFAIK it should be in the latest official version in ModDB (or in the latest Dropbox version, there is where the latest updates to it are).
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.