It sounds as if it might work if the singers are well placed and are balanced matching each other for volume. I suggest suspending the mike so it is hanging just above or in line with your heads and forming a semi circle below or a boom placed in front and gather close together around it. Remember the more distance between sound source and mike the more probs with obtaining decent undistorted balance and gains. Only concern is 400w per channel may not be enough to handle outside conditions and put out enough volume to be heard properly.