I have heard ( read ) before that the 670 doesn´t support quad sli so far so maybe there´s a issue with drivers and hardware. Should be ok in triple sli but quad not supported yet in drivers might be causing that problem. Seems like nVidia will allow for 670 quad sli later on.
Other than that, never heard about this red screen bug/problem...
Try nVidia support since it should allow that fourth 670 just for physx, otherwise it just won´t work or at least until driver support for quad is enabled it will continue to have these sort of issues.
Hope you get it fixed, quad sli is just mad!
That is a fast machine for sure, hehe!