The Ars Nova Caf has enjoyed massive success since introducing its signature closed-mic night, coffeehouse manager Peter Haney, 38, said Tuesday. 'In August, I did away with the Monday Night Amateur Showcase,' Haney said. 'Since then, Monday has been our busiest night. Who would've thought that people prefer conversation to bad acoustic-guitar music and wretched poetry?' Having noted the success of the caf's Absolutely-No-Live-Entertainment Monday, the bar next door recently announced plans to launch No-House-Band Saturday. 