Here's another shortcoming about double-blind tests. They are TOO SHORT.
This does not invalidate whether people can or cannot hear differences within a two minute span.
Can anyone here - I assume you are all into how equipment sounds and
care* - say that they've hooked up a nice system and after two minutes determine that you like it and never had a system that started to grate on you? It sounds great but then after time you hear things that started to bother you?
You have to come here and say that your initial impressions on systems are absolutely valid and
stay the same no matter how long you listen.
*When I worked in a Flagstaff hotel, in the maintenance workroom, the guys there would blast their awful giant Bosewave to distortion levels that I couldn't tolerate for more than a minute. They loved it and could listen to it for time periods that would have made me go crazy. Go figure.