I think you are probably stuck with getting a newer version, tho if NTBackup sees and uses the drive, BackupExec should
You can generally find older versions on EBay for cheap. V9.0/v9.1 use the same serials and should support your environment OK.
(The HCL for both v8.5 and v8.6 say that they support LTO drives. What version are you running?)