I think you'll find you'll be wondering what else you can put in your machine.
I'm using a similar Antec High Current Pro HCP-1200, mine seems to look a little different for some reason, to power an overclocked i7-3930K and a pair of GTX580s. I've seen it draw up to 750W, but will regularly draw 660W, while gaming from the wall socket.
I also have a Xeon system with twin E5420 CPUs, this system has a lot of hard drives and a GTX550Ti. This system runs off an ANtec 650W supply. This system is used mainly as a game/file server but when I ran the Intel Burn-in test, it ran to about 300W.
All in, I think your system will draw in the region of 700W-800W. That's 400W for the GTX690, upto 280W for the CPUs (140W per cpu) and 30W-80W for the rest.
EDIT: Just noticed in the cpu specs that's it's Bulldozer and was released June 2012. I have to question why you're being handed a system where the processors are less than a year old and cost £1000+ each, my instinct is that it's broken.