I'm going to have to disagree with John and everyone else who wants to simply close mic an orchestra. And I don't think you'll get a good sound where the conductor is. You need to go back further in the room.
This applies to bands, orchestras, choirs, classical singers, etc.
In any case, I would believe the conductor is doing something terribly wrong if the strings are getting lost. Of course, there's always you, the engineer, who may want more out of a section than the conductor intends, which I feel defeats the point.
My choral conductor no longer records with our former recording engineer because he apparently refused to put the mics in the audience. We presently get recordings from the house ceiling mounted condensers because it sounds just the same.
But anyways, yeah. Put the two mics as far back as you like. No real need to hook up a mixer unless you want to use more than two mics, but I don't think that's necessary.