The brochure states that there are two processors in the Axe-Fx II, one being entirely dedicated to processing amp blocks, and the other for everything else.
So according to that, placing two amps blocks in a patch shouldn't decrease your available CPU load at all. It should remain exactly the same as it was before you added them, since the amp blocks themselves use their very own, independent processing resource.
Unless dsp 1 + dsp 2 = total resources
I've not looked closely.
Just numbers though, principle is the same.