Because the newest dash is 9199 (or whatever) and XBR is currently still on 8955 you can't plug your legit HDD into the jtagged box.
You should make a USB stick memory unit on the legit box, copy the DLC from HDD to USB, then use one of the usb reading utilities you can find on this site to read the contents of the xbox360-created USB stick to your pc, get ANOTHER usb stick and copy the files onto it, then onto your jtagged xbox.
You can skip the last, pc-to-usb part, if you want to ftp to your xbox
AFAIK the only way to get DLC off a legit HDD right now is either using a HDD reading tool on the pc or using the USB stick method, the USB stick method is much simpler, imho.
Don't forget to grab the latest title update for your game if one is available.
This post has been edited by locvez: Yesterday, 08:22 PM