Well, this is easily enough done. I've taken A/B/X tests many time comparing things in audio systems. Some surprised me when I couldn't distinguish things I thought I would, but distinguishing differences in soundstage (with speakers, not headphones) between tube amplifiers and solid state is quite easy. Have you never critically tried listening for these differences?.... For this reason, folks need to do a blind test first, prove what they say they are hearing (soundstage, sounding like live concert, etc.) and then we can talk about how to measure it.