You have to Download the DLC´s Manually and then FTP it to your Box.
It goes in the Folder:
Content/0000000000000000
Then you open XM360 and there will be the DLC´s, Updates etc.
Wich Version are you using?
Newest hopefully
The Update should be working by Stick!
Probably you copy the wrong Folder.
Path is just :
$SystemUpdate/many different Numbers....
No Upper Folder (SystemUpdate) you have to take the fist folder "away" .(Sorry my English isn´t that gut either

)
So again just $SystemUpdate/and the Files.
Never transfered a Update via FTP guess it´s not that easy?!
And Mate... Theres a thanks button

Would be nice
Greetz Seb