nic, if your preamp is overloading but your microphones are OK, do NOT set the -10 switch on the microphones! Instead, use in-line resistive pads (attenuators) at the inputs to the preamp.
The difference is this: Microphones always deliver a certain amount of inherent noise along with their signals. When you switch a microphone's pad on, its signal levels go down by 10 dB but the potentially audible part of its inherent noise remains essentially unchanged. Result: You've just raised the noise floor of your recording by about 10 dB from what it could have been.
If on the other hand you use a resistive pad at the input of the preamp, that pad will reduce both the signal from the microphone AND its inherent noise by the same amount at the same time. Result: You've preserved the full signal-to-noise ratio of your microphone.
The pad switch on a microphone should be used ONLY to prevent overload of the microphone itself by sounds that are too loud for its own internal amplifier to handle. You want the signal in the mike cable to be as hot as it can be, to help ward off noise from interference. Then if you have to knock the signal levels down at the input of the preamp or recorder to avoid clipping, that's when and where to do it--but never at the microphone, unless the microphone itself is in danger of overload.
--best regards
(and apologies for my DIDACTIC USE OF CAPITALS, but the above is important, and I would like people to hear me shouting all the way into the threads on both sides of this one!)