Can Xencast PX60 and Xencast PX90 be mixed to get shore in between?
I would have thought so no?
So mixing equal parts of each would get you something around 75 shore.

The official answer is that they cannot be mixed but from our own testing, we have found that by mixing the two part As together followed by the two part Bs and then combining the two pre-mixed part As and Bs together does seem to work and does give a mid-level Shore Hardness; you would need to experiment/test to assure yourself that it works for your application and follow the advice above about blending together.