I heard the Synergistic Black Box demonstrated at AXPONA a few years ago (I have not heard the PSI). It made a very subtle difference and I actually liked the sound better with it turned off. Some other people in the room seemed to hear more effect than I did and some said they really liked it.
I've always been somewhat suspicious of Synergistic but that demonstration was very interesting. It was conducted by Ted Denney, the founder. I couldn't hear any difference with the HF-Ts but when he demonstrated the FEQ tower gizmos (the older version) I had to pick my jaw off the floor. They made a huge difference in the soundstage - improving it in every way. I hope to hear them again. It was one of the most impressive demonstrations at the show.

