Right, so there's some outright wrong stuff in this thread now (DOOD64's post for adding the Final Lap Music has outdated copy/paste text and that sent me down an hour long hunt for why my WAD wasn't loading) and a severe lack of highly integral minutia to the main post (why I was following DOOD's post in the first place).
So, to help other folks who may be confused by this mod, here's what got me started:
First, you're going to need SLADE
: http://slade.mancubus.net/
(Sure was fun to find that buried halfway down the comments without a link in the comment that mentioned it, but I digress.)
Download the three files in the OP. Extract all of them wherever is most convenient and organized for you. To start with focus on
FLMusic's zip file. Run SLADE, in the top left you'll find
New WAD Archive. Click that, then drag and drop all the .OOG files from the FLMusic zip into that pane: they'll be added to the WAD, hit Save As, name it (I just called mine finallapmusic.wad) and voila, you have your Final Lap Music wad!
Now go and open
dynmusic.cfg (open it with Notepad). At the very top you'll see addfile DynMusic-SamplePack.wad, add a line and put in
addfile finallapmusic.wad below it (or whatever you named your one). Then below the
finallapmusic listing, copy paste the bigass list from the
FLMPacklist.txt into that area.
With this done, move the dynmusic.cfg, finallapmusic.wad and DynMusic-SamplePack.wad into your Sonic Kart directory (if it wasn't already). Personally I just put mine into the Download folder with everything else. Join a server like RDX Standard, then just leave and test it out in an Offline race to make sure the music is working.
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"Something broke!"
Bruh, I'm as in the dark as you are. Hopefully my instructions above are accurate, but feel free to let me know if something needs fixing or clarification. It's currently too late in the night for me to bother making screenshots, so good luck.