I had tried it, it seemed kind of awkward and silly to do it with the
sound coming out of speakers, even decent speakers. By "decent
speakers", BTW, I mean a real audio system that you would find
satisfactory while listening to music, not some crappy computer
speakers.
Amazing, the first time I used headphones for ICR2, and could hear cars
coming up on me on one side or the other. Incredible, the first time I
did it with GP2 and could almost feel "inside" the car as it bottomed or
clipped curbs as a result of the sound, with stereo perspective, piped
right into my ears.
Just my own taste, but I'd almost compare it to the difference between
driving a serious sim with a joystick and then going to a wheel and
pedal setup. You think "why the hell did I do it like that for so
long?".
JLE