My solution for ONE WAY transfer in Windows 7 using SYNC is this: Computer 'A' create folder 'A SYNC'. Set this folder to sync with computer 'B'. On computer 'A', create a link or shortcut of the folder where files will be stored in 'A SYNC'. When that link or shortcut appears in 'A SYNC' of computer 'B', drop files to be transferred from computer 'B' into the link or shortcut folder and they should transfer without being duplicated in 'B's 'A SYNC' folder. This only works when both computers are on, otherwise, the link or shortcut is not available for transfer. So, if computer 'A' is your NAS and computer 'B' is your android device, you should be able to overwrite files on the NAS, add new files to the NAS, and because there are no actual files in the android device 'A SYNC' folder of either the NAS or android device, deleting from the android device is not a problem. Even if you delete the files from your working folder on your android device (providing you allow enough time for the transfer to complete), that folder is not synced to the NAS, so no deletion on the NAS. It works for me on Windows 7, but it is basically the same as moving the files to the proper folder on the NAS. The advantage of SYNC is the other computer/NAS does not have to be on at the same time as you drop files into the SYNC folder. When the other device is turned on then sync will take place. If you try this, I hope it works for you and is what you want.
