benzos are GREAT addition to almost every method, and for SN they are better than meto IMO.
SN makes you experience kind of "air hunger" - hyperventilation etc, and body still not getting oxygen. Benzos dull it.
In order to maximize the effect, OF COURSE you don't ingest xanny and SN at the same time. Xan is one of faster acting benzos, but you still ingest it 30-60min before SN. The bigger the dose, the better - HOWEVER, make sure you won't pass out before SN administration- benzos can make you really sleepy when they start acting.