Do not take this personally but that is all a bunch of speculative nonsense. ( Huge hypocrisy regarding this theme. ) Benzos and Opiates are 100% safe. (Here we go again ... ) if you drink a pint of lager you might feel somewhat goofier, right ? If you do drink your body weight in lager you might just die. Yeah ?
I´ve always used , at times abused, benzos and (both ) opiates/oids simultaneously with no negative side effects at all (well ,besides ruining my personal life and making others around me miserable, subsequently absent as a consequence ) .
You might see me as the "The exception " ,happens I am "The norm " (NA/AA centers are there to prove it -majority of people in there ,are there for polydrug (ab)use issues ).
Not discrediting that study 100% for obvious reasons ,but the Big majority of people in here know perfectly well that , therapeutic doses ,it is perfectly safe to combine Opiates/oids + benzos ... a lot would even use 1st generation anti histamines and others ( again ,moderation and common sense ) to add to
the sedation/oblivion .
You just have to do your research and use common sense ( as much as possible that is. ). Plus, chances are your Psychiatrist ( or whoever writes your prescriptions ) will back you up on this. Mine certainly did when I appeared with "Sleeplessness " as a side effect to Buprenorphine. Wrote me a script for Oxazepam right on spot and told me when and how to take it - that is part of his job description if I´m not mistaken.
As for the Psychosocial aspects of it ... " Cases of air rage " and all that ... . Neither benzos nor Z drugs cure "bad manners " and other pre existing personality traits .
I apologize if that sounded personal since I´m hardly "shooting the messenger " in here . It´s just far too many years of , on and off, addiction ,and to such combos in particular ,to let that one slide ... ( that and endless hours ,flying from here to there , under the influence, witnessing "normal people " unable to control their alcohol, thus abusing others as the consequence , all this whilst I nodded away peacefully, oblivious to their antics

) .
Take care .