I was also using Stuffit (5.5) originally, but I just gave it a try with good ol' standalone MacBinaryⅢ and that worked too. It should go like this: https://imgur.com/a/YKd4Zvs (first three screenshots)
Once it says Done you can trash the installer. There will be a new folder in the same location as the installer, and within that folder you can run `MacRelix`.
The last two screenshots are me using the `sbin/upgrade` script from within the first Relix flavor to fetch a second Relix flavor.
Thank you. I was finally able to install it, I think my setup is to blame for all the issues. I think I wasn't able to open the .mbin because I downloaded it on Linux before moving it to the emulator, and it missed some information in the process. Downloaded it inside the emulator using iCab, and after several tries (probably because networking on my emulator doesn't work properly) was able to open it on StuffIt 5 and decompress the .gz during the installation.
Once it says Done you can trash the installer. There will be a new folder in the same location as the installer, and within that folder you can run `MacRelix`.
The last two screenshots are me using the `sbin/upgrade` script from within the first Relix flavor to fetch a second Relix flavor.