User friendly volume encryption on NAS?

I am setting up a NAS for a client who needs encryption too. I have setup Truecrypt in the past but it requires the user to manually decrypt the data. Seeing as I am designing an entire system I thought I could implement a more user friendly and efficient system.

Requirements are it has to be 2-bay for mirror RAID, 2x1TB minimum, ability to create a volume which when data is stored there it is automatically encrypted.

So far I have come across the Seagate BlackArmor NAS 400 or 220, from what I gather these use a user-provided USB stick as a key to access the encrypted data. If this stick is lost or damaged there is no way of retrieving the data. This is a slight concern. There is a 3 year warranty on these units.

Or the Synology DiskStation DS210+, I am not sure how the encryption works, it costs more and offers 2 years warranty. A in depth review ere:
http://www.testfreaks.com/blog/revie...ion-ds210-nas/

Does anyone have experience with hardware encryption as with the Synology? I am interested in it but all resources I have found info on have differing info. Can I use any SATA2 DD in the synology to benefit from hardware encryption? Is it password protected?

If anyone has any more suggestions then please let me know.

Cheers