You misunderstood his post that you quoted here completely.
He built his NAS (same box you're using ot store your files) using that mobo+FreeNAS. It does the EXACT same thing your Nas does.
http://www.freenas.org/
It's just the operating system he is using to organize the files on his "NAS" (Such a stupid term I hate it).
In the case of your NAS you linked, it just uses their proprietary nas software.
There is really a lot you can learn about this subject and a lot you can save and make to fit your needs far better than paying 3-4x the price for the same thing you can build on your own.
Same way you build a PC. You put the parts together, and instead of installing windows on the PC, you install a NAS program lik eFreeNAS.