I don't think you need different sound files with Miles... I think you can just set the sounds internally and externally to use different tone, reverb, and other special effects on the SAME sound files.
More then likely u will need 2 sound files. Files will probably be labeled as xeng.wav for external and eng.wav for internal. FSX uses this setup for its sound. 2 files for basically everything. Internal cockpit sounds are in stereo while all external sounds are in mono. FSX also knows what side the exhaust is on to as far as sound. When I pan around a plane in FSX, u can hear the difference when u pan around. Hopefully this is what HTC is gonna implement or something close as it will really enhance the feeling/sound of the planes in the game. Basically making it more realistic sounding.
To be honest actually, FSX uses about 4 files for eng, 2-4 files for prop wash, 2-4 for files mechanical noise (if any damage). Reason is this. At idle, FSX using 1 file that has the idle sound of that plane. For instance, backfire of the engine at idle. 2nd file then would be 1/3 throttle. 3rd file be 2/3 throttle and obviously 4th file for full throttle. Now somehow they take all the files (eng, prop wash and mechanical noise files) and blend them all together to give u the actual sound.