There are two “problems” with null tests: 1) it’s far too complicated for an average “audiophile” to perform, and 2) even when the null test shows that devices X and Y output exactly the same signal, an “audiophile” will look you in the eyes and explain that there is something in the music that is not being captured by the null test but causing a “night and day” difference that wife hers from the kitchen.
For your blind test scenario, people will likely hear great differences even you use the same device in all five positions anyway, that’s why one does multiple comparisons, in random order.
There is an interesting philosophical discussion to be had about the nature of perceived differences in sound. If one believes in, for example, green markers, and paints all of his CDs, and is convinced that they sound better now, then there is something that the marker did for that particular person. It’s just that this improvement is not transferable to anyone else, and it exists quite independently of the marker still bein on CDs or not. Interesting stuff, but rather disconnected from there (not) being any difference in sound waves coming from the speaker.