The MSI GTX 780 TF4 video card you have can run three panels in what they call NVIDIA Surround. Have you not tried that?
The NVIDIA GeForce GTX 780 Ti is a powerful card and if you read my original review of it you can see 5760x1080 performance numbers versus the 290X.
The article is a bit dated, but the performance numbers were vaild at the time and shows that a single card with three monitors runs just fine on NVIDIA. http://www.legitreviews.com/nvidia-gefo ... iew_128012