The egos and rivalries of the great castrati – of Senesino, Carestini, Farinelli – are legendary. Too few arias, too unheroic a role, or just too little virtuosity (Handel’s beautiful “Verdi prati” was almost lost to us when Senesino rejected its simplicity) were all cause enough for a tantrum. How times have changed. Collaborating for their new Purcell project, superstar countertenors Andreas Scholl and Philippe Jaroussky are trading jealousy for duets, and proving that you really can never have too much of a good thing.