There is a beautiful progressive Jewish temple accross the street from Teatro Colon. They do not follow the formal reform prayer book, but the building and their music is beautiful. I would go there in advance to make arrangements. Be sure to take your passport with you and perhaps a letter from a rabbi in the USA, as they check papers and identity (You probably know that BA synagogues were fire-bombed in the past by terrorists, I think in the 1980s. )