You can alter the amount of crew killed for each ship system by adding this to the ships ODF file:
//************************************************** ********************
//CREW CASUALTY FOR SYSTEM DESTRUCTION
//The percentage of crew killed when the engines are destroyed
enginesCrewLoss = 5.0f
//The percentage of crew killed when the lifesupport is destroyed
lifeSupportCrewLoss = 3.0f
//The percentage of crew killed when the weapons are destroyed
weaponsCrewLoss = 2.0f
//The percentage of crew killed when the shields are destroyed
shieldGeneratorCrewLoss = 2.0f
//The percentage of crew killed when the sensors are destroyed
sensorsCrewLoss = 2.0f
//The percentage of crew lost every second while life support is disabled
lifeSupportLoss = 2.0f
Just raise or lower the percentage value for each system to alter the number of crew killed with each hit.
Hope this helps