I can speak for the 3600/4600 models..
Yes, they play off hard discs/usb keys...so far I have added 500gigs to 1.5Tb without problems...even managed to put multiple hd's with a hub...but only 1 at a time can be accesese...
The only problems you MAY run into is that more and more avi's are not encoded the same...so some will play...others won't (again, Samsung, look to adding the VLC to a future update if possible ???)
Please advice whether we can play hard disk movie from blue ray or dvd player USB port