Symphony Silicon Valley, which rose from the ashes of the bankrupt San Jose Symphony, has a business model worthy of its techie startup environment. After five seasons the orchestra is surviving with a rather outrageous arrangement. It has no permanent musical director. Each program has a guest conductor, saving the group a hefty yearly conductor’s salary (Michael Tilson Thomas up in San Francisco costs that symphony over $1 million), and bringing them a fresh musical perspective each time. Audiences are enjoying the variety, as are the musicians who don’t seem to be suffering from the lack of a musical figurehead. The guest conductor model is common in Europe, but perhaps could become more typical in the U.S. as other struggling groups try to find new ways to keep making music.