It's not you being thick, Thrubshaw, there is some mess with these sounds obviously. If you want airbrake sound to be played louder in the cockpit , in the Audacity increase the amplitude of FlapsIn and FlapsEndIn waves or increase "gain" parameter in corresponded sdef files ( gain = 3,2 seems to be fine on my end).
If you want the proper airbrake sound (not used in current version for some reason..) you have to rename Airbrake and AirbrakeBegin to FlapsEndIn and FlapsIn accordingly. I hope that helps.