I recently purchased a dns-323 for my screenplay pro hd player and put Seagate 1.5 tb drives in both bays for a total of 3 gigs and I have had no problems what so ever! I updated my device from the firmware 1.5 to 1.7 and it works great. At first, I was having problems with other issues with it disconnecting periodically, but I figured out what that was and it cleared up after the 1.7 firmware.
I might suggest that you update your firmware to the 1.7, as I have no problems at all streaming media or copying the data from the dns to my computer.
So, are you sure it's your dns that's freezing or could it be the popcorn hour compatibility from the dns? To make sure, view the same files from a computer connected to the network and see if the issues persist. It could also be the data line, router..number of things like over heating..