I know there are a lot of RAIDZONE Open-NAS 4U IDE RAID units coming up for sale after be decommission at many data centers. Also check out Raid, they sell many enclosures (rack and desktop) that carry and IDE interface. 6.8 TB of extra hard drive space is quite a lot. An IDE NAS \SAN works great over an Gigabit Lan.
IMO, you don't want to cram all these drives into a NAS, better to use about a dozen and leave 5 for spares (and in the interim, offline/unplugged they can hold redundant data too, might as well). You can fit a dozen in a full (double-wide) server chassis, just go out looking for something you want to build into.