I'm very happy with Pass X250.5 and N803. It is a very good combinaition. I haven't heard the older series vs the .5 amps, but from what I gather the .5 is a better amp.
I don't think you can go wrong with the X350.5 or the Classe, but I would like to know which preamp you plan on using. As many times as I've heard Classe/B&W N802 combination I was always impressed. But it was always within an all Classe system. So what's the preamp?