Hello Wunk,
Hope this finds you well.
I consulted the PDR (Physicians' Desk Reference), which is THE medication bible that physicians refer to with regard to medications. The PDR lists Zanaflex Interactions as: "May potentiate CNS depression with alcohol, baclofen, benzodiazepines, other CNS depressants."
Because you are taking Xanax, which is a benzodiazepine (a CNS depressant), I would strongly recommend that you consult your physician for the answer to your question.