Can you provide some additional details on what you are trying to optimize?
The odrive backup feature should let you backup whatever directories you want. Are you saying that you would like to take the drive letter as the source instead of a directory within the drive letter. So, for example
X:\ instead of
Are you needing backup concurrency just for the initial backup, or for future backups, as well?
Once the initial backups are done, future backups will be incremental. The initial backup of several terabytes will take quite a while, of course, but after that things should speed up significantly.
Since you are working with shares, you could run odrive on multiple systems/instances, each targeting a different share, to achieve backup concurrency.