How to assign 2 taxonomy vocabularies in a single field for a node?
Usually is is not good to rely on modules what are not widely used (like Combined Termref), because of worse community support and maitainance.

Consider using Entity Reference module what can connect any type of entities together. You can use it almost the same way like Term reference field.

There propably will be some differences in configuration, but nothing critical (blocking use-cases), just less straightforward. Internally it will works the same - is saves entity ID of term into "term reference field".