IIRC, install in the SRB2 Kart folder, then simply use the OpenGL launcher (not the default launcher) to use the models. Of course, if the model is for an add-on character, you have to install and activate that add-on character. Those are separate downloads.
Thank you Spiegel that resolved finding the extra characters, but the main problem of not having access to the characters in this particular pack is still present.
So I have the bonus characters, but I can't find where this packs dlc characters are.
Maybe some guidance on how to install the pack properly on mac might help?