Mixing benzos and opiates is not recommended, tho doctors do it fairly often. Not the safest thing, and I can personally attest to a shitload of accidents, from minor to major, by combining the two.
Quit while you are ahead: if two roxy 15 and 2 footballs (1mg ea) or bars (2mg ea) of xanax isnt holding you, chances are you already have a thousand dollar a month or more dope habit.