Well then, about all you can do is... just put the SP B1's on stands, turn them on, and move them around the room until you find the spot where they sound best. Good luck.
You put one B1 on the vocalist and one on the piano.
OR use the two microphones in a ORTF or XY Pair a distance away. That will cause you to be recording the room as much as the singers. How good is the sonic quality of the room?
Trying to put two microphones on the piano and stuffing the vocalist inside generally will not be acceptable to the singer.