Good question..I don't know! I haven't followed the evolution of the rectifiers very closely. Do you prefer the Dual Series 1 in both tube and silicon modes?
I remember reading that some folks preferred the sound of the Series 2 Single over the Series 1, but I thought that the biggest difference was in the construction topology (mounting of tube sockets and stuff), not the design of the circuit. But, as I said, I haven't followed it. I guess I will now!
I'm anxious to hear from folks who've played both!