By default max is set to work in single GPU mode, however if you manually add 3ds max under the "manage 3d settings" panel in the nvidia control panel you can force alternate frame rendering 1 or 2 mode. It definitely boosts GPU utilisation & viewport speed for me. Previously my 2nd GPU would have 0% load moving around heavy scenes, now has roughly the same load % as the 1st gpu.
Running 2x Titan X Maxwell cards.