This is the extent of my success using nand emu (usb) for rockband2 DLC
first of all im using hairy ballsagna's pc tools to get the .app files for the nand (you have to decrypt them for your console ID).
RB2 from what i know is \title0010005 on the nand. Now there are 3 folders inside, I'm assuming that each one represents a different Gen of DLC (I used the real nand and downloaded songs from the music store to see where they went, dumping the nand after each one).
So using that I dropped an entire Gens worth of app files into the proper folders (i think). When i start up RB2 using the emu'd nand I get a wii system memory full after the main screen and cannot go any further. so basically i deleted a crapton of those files which reduced the folder size from about 5 gigs to 1gig worth of .app files. That actually worked. I got past the main screen and even tested out the DLC to make sure there were no licensing errors. The loading screen in the very beginning takes a while, but thats more than worth it if I could get this to work properly.
Just so you know, I'm using a 150g external HDD with a fat32(25 gigs)/wbfs partition, I'm going to try new things tonight and see if I could get some more done.
It seems like some people know how to do this but don't care to let anyone know how they did it (that youtube video for instance)
So maybe if i (and people reading this) can try to mess around with this, we can figure this out and get a guide up. I know its possible, but maybe not in the method I'm trying.