I don't know what the latest version of PriiLoader is but I do know you can update it from inside PriiLoader itself if you are connected to the internet.You said the above in the modmii neek instructions. Doesn't the latest 8.1 priiloader allow booting the dol for usbLGX directly rather than a forwarder? I think I read somewhere that it would work that way. If not then I guess I need to figure out how to make the forwarder work. I installed a channel forwarder originally in my system menu to boot UsbLGX directly but when I "installed" the only USB Loader GX listed in priiloader it didn't work. I'm not able to check at the moment but I'm pretty sure I don't have the latest priiloader anyway and will update that later today.
I think there may be issues if you tried to boot the USB Loader GX dol itself but I can't remember. But using the forwarder dol will make it easier to update and manage the loader overall and is what is recommended. You can download the forwarder dol from here.
https://sourceforge.net/projects/usbloadergx/files/Releases/Forwarders dols/
Let me know if you need anymore help.