This is a first draft, so please: use the comments section to ask questions about FMOD only. I'm going to do something a little bit unusual and delete off-topic comments on this post so the entire comments thread is FMOD specific. FMOD integration with X-Plane is complicated, so it would be really useful to know what needs more explaining.
There is one more piece of the FMOD puzzle that is missing - Tyler is working on it now and hopefully we'll have it live soon: the FMOD starter project.
The short version is: to get an FMOD project that will properly integrate with X-Plane and other third party FMOD aircraft, you need to get a starter project from us - it will come with the mix buses already in place and set up for X-Plane to use them; you can just add signal processing, etc.
What makes this tricky is: everyone needs a unique starter project or else multiple FMOD aircraft won't be able to coexist. (And that would be sad - one of the really cool thing about FMOD-enhanced aircraft is that you can finally hear the AI aircraft. It adds a ton of depth and realism.)
Tyler is working on a download link that dynamically creates a unique FMOD starter document to avoid FMOD conflicts between AI aircraft. I'll post when this is up and running.
In the meantime, the docs hopefully answer some questions about how aircraft like the Cessna work.
Right now FMOD can only be used to add sound to aircraft, but we are looking at adding FMOD to scenery, as well as our own ground vehicles.