At one time I was running the CTDP sounds. Now I'm using the default BMW sounds.
The only thing you need to replace is the FormulaISI.sfx file.
I keep the copy I use on my desktop and each time I do a new 'change log' I just dump the .sfx and replace it with
the one I prefer.
Im at work now....but I think it is in the gamedata/sounds/vehicle folder.