After lots of frustrating hours, 1 return of the DNS 325, and now a beta firmware update I have successfully moved thousands of files in folders to the DNS 325. I'm not sure if the new beta made it work but what worked for me was going to the finder then GO>Connect to Server>and putting in afp://192.xxx.xxx.xxx/(Folder Name). Once that mounted to my desktop I was able to drag and drop folders with files to the NAS with no issues. I didn't have to split up large files or folders. I literally transferred 750gb to the unit with no errors.
I wish MAC directions had been more clear in the manual or anywhere for that matter but after some trial and error it is working just fine!!