I can tell you that I've successfully installed the homebrew channel as well as the USB Loader GX on my Wii 4.0u console. I've created a thread explaining how I did it here:
http://wiinewz.com/forums/wii-hackin...-4-0u-wii.html
From what I've been reading in my thread, I'm not the only one successful in modding a 4.0u Wii.
Perhaps you can give it a read, and if it seems helpful to you, you could give it a try. All I can say is I didn't have any problem with the process I followed (I detailed it in my thread), and I was VERY green when I did it...
Good luck with whatever path you choose.
CWAVE