Double blind is meaningless to me. If you were to participate in a test of that type, I think it would be invalid because your brain would be racing trying to hear differences, and doubting itself. There are so many unknown variables about the way a brain processes an event like that.
I believe that there are amps with sonic differences that are very easy to hear, and others that are more subtle, but it is best to listen to any amp over a period of weeks with all different types of the music you like so that your mind can build a profile of the gestalt, and whether it is right for you.