[filipv]

If you're recording and things just don't work out, then try not to record with mics corresponding to distinct SATB groups of singers. Instead, try shuffling the choir members, so a baritone sings next to a soprano who sits in front of the altos and so on... diffuse the singers physically as much as possible. The end results may be better. If the singers are good, they should be able to do it.

I once needed to record a large mixed choir (50+ people) using only two U87s. The recording sounded good only after I convinced the conductor to shuffle the singers around.

Also, bear in mind that choirs consist of many people: not all of them will sing their best on the exact date/time of the recording session. If you notice one or more singers just don't sing right, pitch or dynamics-wise, politely ask them (through the conductor!) to take a break and try to record without them. It's not at all an inappropriate thing to ask. It's not uncommon for the conductor to do that in a rehearsing session. Since you're recording, you should be even more strict.