I'd suggest putting a removable hard drive setup in a CD bay and keeping two sets of backups, one always offsite (like in a safe-deposit box). There are removable setups that either take the hard disk bare or mounted in a special tray.
I don't believe DVD's are a good backup media as they don't age well and the failure rate is very high. At less than $100 per TB the harddisks are much cheaper than quality DVDs, an order of magnitude faster, and more reliable.
Your external box doesn't seem to give a proper fire rating, though the website mentions one, and may not be enough protection in a real fire. There should be a temperature vs time rating. RAID setups only protect against a single drive failure and not things like controller or powersupply failures, multiple disk failures, etc.
Specifically for data loss due to theft of the media your external box is no real protection from theft since the whole box can be stolen easily. Securing the data itself is another issue but for myself I'm less worried about crack-heads selling my pictures than I am about being unable to sell the pictures myself because some crackhead hocked the drive for fifty bucks.
USB is glacial for disk access and can be a hindrance to keeping a good backup routine -- I personally don't trust any windows based auto-backup scheme as they seem to be disfunctional.
My setup may be a bit of over kill for most photographers but I have raid 5 arrays for on-line data and two complete backups to relatively new hard-drives. One set of backups goes in a large (100 lb) locked fire safe in the basement and the other is at the bank. The external arrays are connected by ESATA and are actually faster than internal arrays using the motherboard hard disk controllers. If I'm going away I can unplug the external arrays and fit them easily in the fire safe, leaving only the OS drive and SAS work drives in the computer itself. The RAID setup is for the protecting my most recent work from a drive failure that seem to average about 1 in 20 per year. I'm dealing with around 6TB of data.
For what it's worth........
Doug