Dan,
At the risk of being flamed, have you played with power cords/conditioners with your Benchmark? I've found mine to be very sensitive to such treatments. Are you running it balanced or single ended. USB? From what I have read, I doubt if the PS Audio is enough better to make the switch and the Bryston doesn't have a volume control. The Berkley seems interesting, but pricey(5k) for something soon to be outdated... I too am interested in a switch.
Tobias- What was the input for your comparison of the Stellavox vs Benchmark? I'd love to hear more of your comparison of the two...