I did a tiny bit of looking at the OpenFiler and FreeNAS sites and forums, but I didn't see a decent hardware reference guide for either of them unfortunately. In the end, I don't mind doing a little work up front, but I don't want a difficult to maintain frankenstein system. I'd like a somewhat power efficient footprint with enough space for 6-8 drives, hopefully without too much headache to access them physically (replacing, adding new, etc.)

If I'm going to be installing my own software to run everything, I'm also not going to be looking to spend $600-1000 on a suitable case & mobo. At that point, for my needs, it makes more sense to go with one of the off-the-shelf solutions, even if spending an additional few hundred dollars.