A 64' stop really pushes the limits of audio reproduction technology. Its lowest fundamental frequencies are in the infrasonic range, around 8 Hz, which is beyond the reproduction capabilities of most conventional audio systems, including typical PC setups.
However, the issue is not limited to the fundamental frequency. A 64' stop also contributes audible harmonics and changes the overall tonal balance when combined with other stops.
Consequently, the result might sound somewhat different – or even somewhat unnatural – compared to the actual pipe organ, simply because the playback system cannot reproduce the full frequency spectrum and physical impact of the original instrument.
I once had the opportunity to play an organ with a real 64' stop. In my experience, it is something you primarily feel physically rather than hear acoustically. It provides an additional sense of depth and weight, almost as if it completes the sound from below. To me, this is quite different from the impression created by a digitally reproduced 64' stop. The physical sensation is an essential part of what makes it special.
I have also found that 64' stops in some sample sets don't sound particularly convincing or authentic. Of course, this may not be entirely due to the samples themselves. Capturing and recording such extremely low frequencies, as well as reproducing the acoustics and physical impact of the original instrument, must be quite challenging in its own right.