OBD II mystery and legend continue, although it seems that companies such as Dinan, and the guy in Salt Lake whose name escapes me, but refered to as Shark chips, have done a good job with BMWs with OBD II. You are probably right about the numbers being low for FXs, especially 45s. There will be more available for the 6 cylinders because of the Z and G35 market.
I wish Nismo had something like Dinan that would permit retaining the factory warranty.
On the exhaust question, I am not looking for something obnoxious, just richer, mellower in sound (all very subjective). The problem is that unless it is engineered correctly, one may gain hp. and lose torque (usually too little back-pressure). The modified Lexus I ran in One Lap a few year's ago had the resonators in place, no mufflers, and Borla carbon fiber (mufflets I will call them) tips and had a very sweet sound. Perhaps a company wanting to create a special FX for SEMA would be interested.