The only difference between those two part numbers above is the software included in the hypervisor datastore. The K9 includes export restricted code, while the XU version has export unrestricted versions.
To order user licenses for the BE6000, use the top level part R-CBE6K-K9.
Further details on your questions can be found in the BE6000 ordering guide. (This is located here with the other Ordering Guides)