The thing about psychological bias is that it is unconscious. Just because you think it is going to do nothing doesn't mean you are pre-disposed to hear nothing. Thinking it will do nothing is conscious bias, not the same thing.
So there's plenty of reports saying 'I don't except to hear any difference but I was shocked.'
Likewise when you try something full of expectation for the improvements it is going to bring and it actually sounds worse to you. Hoping/expecting it to sound good didn't change a thing.
You can't consciously decide what impression to have. Otherwise we would all just use cheap Amstrad midi-systems and be well happy.
Current Lash Up:
TEAC VRDS 701T > Sony TAE1000ESD > Krell KSA50S > JM Labs Focal Electra 926.