I agree with Oaktown for best performance -
Oaktown wrote:If you want 12 stable HD outputs, get a Nvidia GTX 980ti or Titan Z, three Datapath X4 video processor,and M.2 SSD.
That said, if you're working on a tighter budget and have some time to order and test solutions; then take a look at the NVS series from NVIDIA. They've just released a new 8 output card for digital signage. It includes edgeblending and mapping capabilities built in, so if you're not looking to use the more advanced VJ features of Resolume like layering, effects, and BPM syncing then it may be a more stable hardware based solution.
Unfortunately, I haven't seen any Resolume performance numbers with these cards, but I'm hoping on building a rig in the coming months and testing it out.