Orchestras across the country are scrambling to attract new audiences with such gimmicks as video screens, loquacious conductors, and hot young soloists, but much of the experimentation is in the trial-and-error realm, since there isn’t a lot of evidence concerning what works and what doesn’t. The Detroit Symphony launched a new series this season aimed at cultivating demographics it doesn’t currently see much of, but Mark Stryker says the idea will need a lot of tweaking before it yields dividends. Moreover, its possible that orchestras are barking up the wrong tree with the idea that younger audiences want less substance and more flash.