Read the documentation:
Status
The code currently provides implementations for all the arithmatic operators. It also provides implementations for approx. 140 built in functions in Excel. The framework however makes it easy to add implementation of new functions. See the Formula evaluation development guide and javadocs for details.
So, not all Excel functions are supported out-of-the-box, which seems to include CUBEMEMBER.
You have to implement that yourself then, and you can then help others by becoming a contributor to the open-source community, instead of just a consumer, by adding the implementation to the project.