Yes indeed. Except that we also know that casual and uncontrolled listening leads to false conclusions. So whatever else there is to discover about audio reproduction, and yes I agree there are probably still some things to learn, will be:Yes, we fail to see how it is possible, which is why we need more science! Many people hear things we 'fail to see'. Nice to think it's all in our heads, but I really think that there are other things happening that we haven't figured out how to quantify. Or I could be wrong, but history shows us that the progress of science brings new discoveries where we thought we knew it all.
a.) small in comparison to the large issues of frequency response and distortion, and
b.) not the result of casual listening.
So far the evidence is that the biases from sighed and uncontrolled listening FAR outweigh the other unknowns. That is why people making claims about what they hear at home via an uncontrolled test have no value. I am all for hearing evidence of things that actually exist, but to know that it is something audible a controlled listening test must be done. People who have never experienced a double-blind and well controlled test do not appreciate how it may change a person's life. It changed mine, and others I know, and I have a research background (teach postgrad research methods, double-blinding is a very basic experimental control). The sorts of areas where we still need a lot of research in audio are in proper soundfield reconstruction and room interactions - and this is the wrong forum to discuss that.