One piano, two pianos, four hands duets, eight hands quartets — this concert has it all. FWSO music director Robert Spano and his long-time collaborator Pedja Mužijević, pianist Shields-Collins (“Buddy”) Bray, President and CEO Keith Cerny, rush the stage for more than a dozen high-energy works for multiple pianists by composers ranging from Bach to John Cage and Schumann to George Crumb, with favorites like Saint-Saens Danse Macabre for two pianos, eight hands and Crumb’s “Celestial Mechanics” anchoring the program.