Conductor George Manahan and his orchestra continue their productive relationship with a rising generation of composers and performers. The big news on the Feb 27 bill is probably the world premiere of excerpts from Sarah Kirkland Snider's Unremembered. But a performance of Weill's The Seven Deadly Sins and versions of songs by My Brightest Diamond (co-orchestrated and sung by the band's leader, Shara Worden) aren't anything to sniff at, either.