If all you need to do is copy files from the disks then it can be done with a computer. If your computer runs windows then you need to get Ext2IFS (google is your friend) and install it then you can plug your drive in and copy to your heart's content. If you are running Linux then just plug in the drive and again copy away. The Ext2IFS will even allow you to use an SATA to USB caddy to do the job.
This, of course, assumes your drives are not damaged physically and you have enough space on another drive for the copy.
Once you have copied them, put the drives in the DNS-320 and format them then you can transfer the files back.