GTX 680 4GB problems....

Hi Guys,
Im running a Z800, with 4x GTX 680 4GBs in a Cubix Desktop 4. heres the problem...
If i have 4 cards running, Resolve will play out of the HDSDI but my viewer has a white screen and if i import media Resolve crashes instantly. with 1,2 or 3 Cards resolve runs fine.
It gets a little strange because RedCine X Pro crashes with 4 Cards, but once again its fine with 1,2 or 3.
I didn't think RedCine X used Cuda, so it maybe a driver or some setting on my workstation.
I'm running the correct version of Cuda for Resolve 9 according to the config guide, but it was acting like this with 8.2 as well.

Any Ideas?

Cheers,

Glenn