You should FTP your files to your hard drive then use XboxISO making program to create an ISO of the files then burn with imgburn. If you want to copy a backup you should just be able to do a direct "disk copy" from imgburn.
Edit: Sorry I didn't fully understand what you were asking. Your copy of the backup is fine, all disks will fail with time thats how it goes. Yes you can copy your other backups just like you did the 1st. As long as you have the original and dont use it (ie not getting scratched) then it is preferable that you do like I said in the first paragraph and FTP your files from the original and burn to a new disk.