On NLB image, go to plugins menu and scroll down to NLBPanel
Start that up and you will have control over all the EMU's that are pre-installed in the image. incubus, mgcamd etc.
You can also update the EMU from here, if there is a newer version.
All later versions of NLB have EMU's already installed, so you probably only need to edit the incubusCamd.conf file and ftp it back to the box.
It goes in the /var/keys folder. Personally I find it easier to just telnet into the box and edit the file with vi.
Manually updating the EMU is really easy too, so much so that its almost unnecessary to use a plug-in but I guess it helps non techies.
Simply download a new version from the net, unpack it, if it supports multiple receivers, it might have different versions of the EMU in the download. Look for the sh4 version (this is the right one for the processor in the CubeRevo. Copy this to the /var/bin directory. This file will then override the pre-installed EMU file that would be in the write protected /data directory. So in the case of incubus again, the only file you need to copy there is incubusCamd.sh4 to update that emulator.