I just found this Simphonics website that has software and hardware for soundfile creation for (very) high end systems.
They have a whole series of .wav file downloads located there that are possibly useful for adding enhansed sound environments to the simulated cockpit.
For example, you can write a small program (using FSUIPC) that will play a sound file on one of the "glass cockpit" computers that will output to a speaker located in a specific location upon a specific event. So you could put a speaker in the floorboards of your simpit and have a landing gear sound come from the floorboards when the gear deploy or retract. Turbulence could also result in a little "thumping" coming from there (and other places). Talk about adding some realism!
Check out the vast number of possible aircraft and environmental sounds located at:
http://www.simphonics.com/library/Wave%20Files/Aircraft/
best,
.................john