There is a yet rarely used technology called "explicit multi-adapter rendering" if that's what you mean.
It requires every single application to be coded for that.
Here are some links:
Those 2 samples didn't knock my socks off though
I vaguely remember this being possible at one point. This was way, way back in the days of the Z68 chipset. If I am remembering correctly, it was facilitated by a third-party software package called Lucid Virtu. I don't remember whether a similar capability was made available subsequently. I believe that Lucid had a patent on this that may be preventing others from delivering the capability...