3,000 in a church! well, this one is big, no doubt.
The issue of recording chamber music is tricky to say the least. There are many pages in Internet dealing with it, for example this:
http://www.dpamicrophones.com/en/Microphone-University/The-Essentials.aspx
But for tomorrow! not much time, really. I made a few tries for my last audition a month+ ago but finally the recording was not made. But I had reached some (provisional) conclusions:
- Use a good condenser microphone (not a dynamic type).
- get a good brand (AKG, Audiotechnica Oktava and a few other)
- avoid USB types -if you can (and have the phantom supply required)
- Place it at a moderate distance, say 2 meters away from the two players. Not close to your head. You need to capture the violin too, so unless you will use two microphones, the unit should be set at a similar distance from each instrument.
- An omnidirectional pattern should be better (perhaps), but I believe it is safer to use a cardioid type if only two players are involved.
- Use a medium or large size capsule, if available.
_ during my questioning in Forums, I received an interested reply (but was not able to try it): to use two microphones (Oktava M12, I was told) hanging from the ceiling above the duet and record in stereo.
- If on the floor, you should isolate the mike(s) from the floor or other hard surfaces that could transmit vibrations to it(them). Pro mikes sometimes come with a mount that includes elastic bands that keep the mike centred and without touching anything rigid.
You will probably have to break many legs (that is, have lots of luck) as for the recording goes. Wish you the best.
<Added>You could rent a suitable microphone and power supply in your area, but time is really short, so you probably will have to do with what you already have.