hi rvwear:
when there is a blind or double blind test, statistics is used to evaluate the result
statistics delas with probability, not certainty.
when you are talking about knowledge, truth and certainty are required. a mathematical proof is required to determine whether something is true.
when you are talking about differences in sound between one component and another , and whether the difference is detectable, some people can detect a difference, while others can't. thus there is a probability that a difference can be detected. probability is not certainty and hence knowledge is not established.
however, one may have confidence that powercords sound different. one does not know with certainty that powercords sound different.
when dealing with probability you are dealing with opinion.