Confirming that it is the nature of SQL and if combine to streams is not used we will need to have 6 parallel streams to restore directly into SQL Server. If combine to streams is used, we will stage the data back to Job Results (or staging directory if set with additional setting) in order to create all of the backup devices (i.e. .bak files) to allow restore from all devices simultaneously.
You can actually avoid this by performing an AuxCopy back to a disk location and then adding bDisableAuxCopyRestore additional setting to the client:
Note that when you add this, use the MSSQLAgent category instead of Sybase.