Thanks for all the excellent advice. I seem to be homing in on a workable,
compact solution, which would mean using the Minidisc player as the recorder
and forgetting the PC. I have an old pair of National Panasonic WM-2244-N
microphones (bought as a pair, reference RP-8135). They are "low impedance"
500ohm dynamic, and seem to work OK with the MD player, providing I set
"high sensitivity". That would avoid the need for pre-amps and electrical
power, since the MD player will record happily for long enough on its
internal battery coupled with a piggy back alkaline AA.

My only concern would be whether the mikes would be sensitive enough when
placed, say, 40 feet from the centre of the choir and orchestra. Might it
help to make the mikes more directional if I place some kind of cones around
them?? Or an umbrella behind??

Thanks for any more thoughts.

Steve