I am having a similar issue! I can't get my back up copy of RB2 or Lego Rock band to find my guitar or drum kit. But I can get them working with my legit Beatles edition so I know they work.
I'm using NeoGamma 7. I'm looking for either a way to enable the USB or get them to work, maybe a priloader or something, or if there is a diff emulator then neogamma to use.
so....bump! cause I could use help with this too.