the pre-made emunand is fine.
What you need to rebuild (or replace) is the content of the /sneek/ and /bootmii/ folder.
Bootmii always launch the "armboot.bin" located on SD card.
So, how do you think neek knows that you want to load the folder on USB instead of the one on SD if there's no option anywhere to tell it the path you want to use?
if you rely on Bootmii to launch Uneek, you still need some files for the SD card. You can't use only files located on USB.
So, if you want to use EmuNAND folder located on SD, you use the "Sneek" prepared package which should come with a "put no SD" folder.
If you want to use EmuNAND folder located on USB, you use the "Uneek" prepared package which should come with BOTH "put on SD" and "put on USB" folders.
Sneek:
sd:/bootmii/armboot.bin <-- the one which tells to use SD
sd:/sneek/kernel.bin
Uneek:
sd:/bootmii/armboot.bin <-- the one which tells to switch to USB
usb:/sneek/kernel.bin
If you use USBLoaderGX to boot into neek, it doesn't rely on "armboot.bin" at all, and loads the correct kernel.bin located on the expected device based on your EmuNAND location. so you don't need files on SD to use Uneek.
If you use Nswitch, even the latest version is not good. Nswitch uses armboot.bin on Wii, and the same method than USBLoaderGX on vWii. So, if you are on Wii, you need the armboot.bin (for the correct device) on your SD card.