A good way to combine disk-to-disk and tape backups is to use Policies.
Within the policy, you will create two templates. The first template backs-up to disk, then a duplicate template backs up the same data to tape. While the tape is working, the next d2d job can begin.
Tape restores are directly from tape...no need to go back to disk.
You can experiment with policies using a small backup to a quickly overwritten media set.
This way, you can duplicate your incrementals to tape on a daily basis. Just put them on tape that has a planned overwrite period.