For fans of forward-looking, contemporary classical music, two concerts this weekend offer a bounty of exciting, rarely performed works. Both take place in venues that serve booze and aren’t the sort of tony spots you’d expect to hear string quartets, but on Friday Ensemble dal Niente presents “Hard Music Hard Liquor” at Mayne Stage, while on Sunday afternoon the Empty Bottle hosts the latest installment of the (Un)familiar Music Series, curated by Doyle Armbrust of Spektral Quartet. The second is a benefit for the great New York label New Amsterdam Records, whose offices and most of its stock were decimated by Hurricane Sandy, and it just happens to function as a veritable roll call of Chicago’s new music community.