Why would you want a soft synth to recreate piano, choir, brass, and string sounds? I think what you need is a VST like Kontact, Giga, Halion. They'll give you very realistic sounds but the emotion and life will have to come from you playing them correctly. VST's are great tools when used correctly but even a great sound not played like the real instrument won't sound good. It helps if you know the nuances each instrument can create, the key range, and scaling.