Interesting, what are you using at the moment? single USB capture device, and software that transforms/duplicates the image for the Rift?
You may have seen about this:
Allows live 3D FPV with the Rift and other HDMI-based goggles or monitors. Been doing some tests lately (not with a Rift at this point) and getting great results. Advantage being no PC-related latency, "bluescreen" or reliability issues