There are phase problems you should take into account. They could come from a variety of sources, perhaps the amp, cd or dvd player or speakers. They are VERY audable even if out of the hearing range. In general, the wider the bandwith the better, but not at the risk of increased phase shift.
John, not at all like that. Take for example the original cd playback units. They had a ruler flat frequency response from 10hz to 22khz. Should sound perfect, was the thinking back then. They didn't sound perfect. In fact, they sounded terrible. Why? Digital filters at half the sampling frequency or 22.05khz (44.1k sampling) These anti aliasing filters are very sharp, brick wall type filters, thus they had severe phase shift(smearing of the audio image) throughout the high frequency range. Took them a few years to wise up. Then they started oversampling (88.2khz or 166.4khz) so that those steep filters could be placed further out of the range of human hearing. Our ears are much more sensitive to phase than to frequency. It dates back thousands of years. Lets say it's 5000 years ago. Your walking thru the forest when suddenly, a spear goes whizzing by your head. Ask yourself the following question: Is it better to know the direction or location that spear came from so you can run like hell in the other direction or what frequency it whizzed by your head at? Again, phase smears image, thus fooling your brain into not knowing where the sound came from or when. Understand?
Yes, I understand. I fact I have been trying to tell people that phase is everything - it is how we perceive the direction of sound - on "Teaching an old dog new tricks..." and "Plunging into mutichannel". That is why getting your speaker delays right is far more important that "Bass management". But outside the frequency ranges we can hear, we have no phase information, either.
BTW I think you underestimate how old phase is. Fish have a "lateral line" system instead of ears, and it does much the same, as I understand it. When you get to mammals....
Do people know bats are practically blind? But go and watch one on the hunt. Awesome. It hears reflections (echos), from flying insects, of its own frequency-modulated sweeps. The phase of the reflections it gets back gives it information on the trajectory of the flying insect, its prey, when the bat itself is flying. Look at the size of their ears. They can hear to 100 kHz.
If I were a bat, I would definitely be interested in 192 kHz sampling frequency!
There could just be something in giving your speakers a higher frequency than 20 kHz, though. You can't hear it, but it could affect the way the speakers perform to give you the stuff your can hear. In any case, I cannot see how going up from 48 to 96 kHz can make any difference. Unless you have 96 kHz speakers. And 96 kHz ears. Like a bat.