I have more history as a collector than taper and currently have a FreeNAS 8.3.0 box (AMD multicore cpu and ASUS motherboard, 8gb ram, 6 x 1tb disks). About 3.7tb usable space. I use raidz2 (4 data + 2 parity )so any two drives can fail and I'm still good. If you're comfortable with managing a linux box on your own I recommend FreeNAS but definitely play with it before you put important data on it. Memory is important on this so this is no longer something you can relegate your 5 year old computer to.
I used to have 6 external usb disks and got sick of moving stuff around and backing it up to other disks, etc so I went the FreeNAS route and cracked all the disks open to put them in a single case. I also had a few 2 tb internals in another box I used as temp storage. One thing to keep in mind going this route is that for raid the system only recoginizes as much space as the smallest drive of any others in the pool. So i started with 4 x 500gb, 1x 1tb, and 1x 1.5 tb which the system treated as 6 x 500gb. over time I got each 500 gb drive upgraded to 1tb and magically the whole volume grew to 4 x 1tb space available. Now I need to go to 5 x 2tb disks and get 6 x 1.5tb, then full 6 x 2tb.
Although this device is very redundant disk-wise within itself, I still need a second freenas box to mirror to which I blew the budget on many times over to buy microphones and preamps and recorders and..... if the CPU or memory ever takes a crap it's possible to hose the zfs system, or have the whole thing burn up or something.
A freenas box can share to almost anything in one form or fashion. I have some old Xbox's mod'd to run XBMC which I can use but haven't recently, and XBMC is now well ported to run on standard pc's so it's a good option to connect to an entertainment system.
Not exactly what you were looking for but the freenas is applicable. I like it and think ZFS is f'ing cool but you definitely need to be ready for what it takes to manage. It's a DIY solution for sure. I've heard good things about QNAP on the other hand.
At these volumes of data you're really getting into the realm of Production data center/data warehouse management believe it or not. Same principles apply since you can no longer easily move the data temporarily to another external usb drive to make changes. You need to test upgrades on backup or redundant systems before messing with your Production system. make sure you notice when a drive fails and get a spare installed before you lose another, hope a second or third don't die during volume rebuild, etc