Overcoming Crippling Syncing Limitations

Using ReadyNas 214 with OS 6.2 Firmware 6.6.2. My remote computer is a MacPro with OS 10.11.6

I want to define the specific location of the sync folder on my computer as well as on the ReadyNAS. The ReadyNAS sync function does not seem to be able to see any of the hard drives where my data resides on my base computer.

My computer has four hard drives. The smallest is the root drive where my OS and applications reside. The remaining three are where my data resides. The ReadyNAs sync function appears to be blind to these drives and only wants to use my root drive.

It does me no good to create another file on my root drive that duplicates a data file that already resides on another drive. That redundancy is what the ReadyCloud NAS is supposed to provide. There simply isn't enough room on my root drive for the data files in any case. And I sure don't need THREE copies of these files. 

How can I tell my ReadyNAS that I want folder X on my ReadyNAS to sync with Folder Y on my computer - no matter on what drive Folder Y resides?

Unless this is possible, the sync function as it appears to exist is pretty much useless. By the way, isn't the syncing supposed to go from the computer to the NAS, not the other way around?