My Wii is at version 4.1U right now. (I did it by following these steps for BannerBomber/HackMii method (3.x to 4.1 method) from GBATemp ). (I started fresh from version 3.1)
I then installed a Homebrew app called USBLoader_GX. It installed OK.
USBLoader_GX came up fine, I was able to see the...