Objectivist audiophiles will point to the lack of double blind tests showing that frequencies above 20kHz are audible except perhaps to the youngest people. For most of my life, I've had a virtual cutoff just above 16kHz.
There are ironclad digital theories, that basically say PCM is better than intuitionists might think. A PCM encoded system (with properly designed filters, etc) cannot be distinguished, technically, from a real one with similar bandwidth and through that bandwidth. So, yes, one can show the various imperfections of PCM using 100Mhz oscilloscopes, but not with comparably bandwidth limited system--they just don't show up within a comparably limited bandwidth. You don't "hear" the pre-ringing, etc, because it's way out there.
Now, there has long been a particular claim that humans can detect leading edge differences that resemble frequencies higher than 20kHz. And these claimed detections go to the equivalent of about 40kHz.
There have been some "brainwave" studies that show correlations with frequencies above 20kHz and up to 40kHz. These are controversial and have not been replicated elsewhere as far as I know.
In any case, it looks like the most we could possibly need is about 40kHz. And at that point, not may speakers will work either. I strive to achieve at least some output there with supertweeters.
So it looks like 96kHz, with it's bandwidth of about 48kHz, is more than we need, even according to the most sensitive and potentially false-positive studies, from brainwaves.
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