That is some expensive stuff. I feel like it'd be more cost-effective to just build a computer that functions as a NAS. I mean, I suppose it's a value for the people that want to just buy a thing that you plug in and it works, but I'd rather use my smarts and my luxury of time to save the money and build my own NAS.
I don't know about the XL version, but the older was listed at $995 diskless back in July, and I saw I guy price the parts in Nov at $773. So you're paying roughly $200 for someone to put it together, tweak the bios, build a custom kernel with the right drivers, and test it. Don't forget warrantees, etc. How long would it take you? What's your time worth? If you can do it in 8 hours (1 day), and your time is worth less than $25/hr, congratulations.
Me, I might do it for fun, but that's an awfully tempting price to just pay someone else to do it.